An Etymological Dictionary of Astronomy and Astrophysics

Same as → 42 Orionis.

See also: Star name in the → Bayer designation scheme.

One of → Saturn’s rings, lying beyond the → D ring and before the → B ring, at 74,658 km from the center of Saturn, with a width of 17,500 km. Same as the → Crepe ring.

See also: → ring.

Same as → charge conjugation and → charge symmetry.

See also: → charge; → symmetry.

An → asteroid that belongs to the family of → carbonaceous asteroids. They are → depleted in → hydrogen and → helium, have chemical ratios akin to solar composition, and show low → albedo (0.03-0.09). C-type asteroids are the most common variety, forming around 75% of known asteroids. They
inhabit → main belt’s outer regions.

See also: C stands for → carbonaceous; → type; → asteroid.

The Sculptor’s Chisel. A small inconspicuous → constellation in the southern sky, representing a sculptor’s chisel. Its brightest star, Alpha Caeli,
is magnitude 4.5. Approximate position: R.A. 4.5 h, Dec.: -40°; abbreviation: Cae, genitive form Caeli.

Etymology (EN): L. caelum sculptor’s “chisel.”

Etymology (PE): Qalam “chisel,” from Ar., related to L. caelum?

1. An enclosure, usually made with bars or wire, for keeping birds or wild animals.
   

2. An enclosed structure resembling a cage. → observer’s cage, → Faraday cage.

Etymology (EN): M.E. from O.Fr. cage, from L. cavea “hollow place, enclosure for animals,” cognate with Pers. kâv “hollow,” → concave.

Etymology (PE): Qafas “cage,” of unknown origin.

A member of a group of tiny (millimeter to centimeter) light-colored meteorites found often with → chondrules. They consist of high vaporization minerals, including → silicates and → oxides of Ca, Al, and Ti, but are quite poor in Fe. Compared to common → chondrules, which are uniformly spherical, their shapes are less regular. They appear to be 2-3 million years older than chondrules. CAI meteorites are probably the oldest solid materials to have formed in the → solar nebula.

See also: CAI, short for → Calcium, → Aluminium, and → Inclusion; → meteorite.

The standard model of → radiation-driven winds in which the acceleration of → stellar wind is provided by the → absorption and → scattering of ultraviolet photons in ions of abundant elements (→ CNO, → iron peak) in the → Lyman continuum. The model was developed by Castor et al. (1975), who assumed that the forces due to the radiative lines and the pressure gradients are functions of local velocity gradient, and used a large number (~ 10⁵) of lines which have a statistical distribution in line strengths. The model led to predictions of → mass loss rates (M_dot) and terminal velocities as a function of stellar properties and the line statistics parameters. With the modifications by Friend and Abbott (1986), Pauldrach et al. (1986), and Kudritzki et al. (1989), CAK multi-line theory gives good agreement with observationally derived values of mass loss rate and → terminal velocity (v_∞). CAK wind solutions predict the terminal velocity to be proportional to the → escape velocity and the mass loss rate to depend strongly on the stellar → luminosity. Observations over the past decades have shown that these main wind parameters, M_dot and v_∞, indeed behave as predicted by CAK. This basic agreement between observations and theory provides strong evidence that the winds from → massive stars are driven by → radiation pressure and this has favored the CAK formalism. See also → multiple scattering. See the review by J. Puls et al. 2008, Astron. Astrophys. Rev. 16, 209.

See also: CAK, the initials of the researchers who developed the model: J.I. Castor, D.C. Abbott, and R.I. Klein(1975, Radiation-driven winds in Of stars, ApJ 195, 157); → model.

A → bipolar nebula and → OH/IR source with technical designation OH 231.8+4.2. It is a → proto-planetary nebula (PPN) 1.4 → light-years long and located some 5,000 light-years from Earth in the constellation → Puppis.

The obscured → central star, named QX Pup, is classified as M9-10 III and has a → Mira-like variability consistent with an evolved → asymptotic giant branch (AGB) star. The late evolution of this object may have been complex since it has a binary → companion star (of type A0 V) that has been indirectly identified from analysis of the spectrum of the hidden central source reflected by the nebular dust. The system has a total luminosity of ~ 10⁴ Lsun and its systemic velocity relative to the → Local Standard of Rest is V_LSR ~ 34 km s^-1. OH 231.8+4.2 is very likely a member of the → open cluster M46 with a progenitor mass of ~ 3 Msun. The nebula is also known as the Rotten Egg Nebula because it contains a lot of sulphur, an element that, when combined with other elements, smells like a rotten egg (see, e.g., Prieto et al., 2015, A&A, 575, A84).

See also: The name “Calabash Nebula” was first proposed by Icke & Preston, 1989, A&A, 211, 409. It refers to the apparent form of the object which resembles a calabash “a tree that has large, rounded gourdlike fruit; the fruit of any of these plants,” from Sp. calabaza, possibly from Ar. qar’ah yâbisah “dry gourd,” from Pers. kharabuz, used of various large melons; → nebula.

A metallic chemical element; symbol Ca. → Atomic number 20; → atomic weight 40.08; → melting point about 839°C; → boiling point 1,484°C; → specific gravity 1.55 at 20°C; → valence +2. It is fifth in abundance in the Earth’s crust, of which it forms more than 3%. It is an essential constituent of leaves, bones, teeth, and shells. Never found in nature uncombined, it occurs abundantly as limestone, gypsum, and fluorite. Calcium has several radioactive isotopes. It was first isolated by the British chemist Humphry Davy in 1808.

See also: Coined by Sir Humphry Davy from L. calx (genitive calcis) “lime (CaO) or limestone (CaCO₃)” in which it was found, from Gk. khalix “small pebble,” see also → calculate, + → -ium.

A discontinuity in the spectrum of galaxies near the Ca II → H and K lines at about 4000 Å. The Ca break
is the most prominent feature in the spectra of elliptical galaxies. Its strength is given by the → calcium break index.

See also: → calcium; → break.

The strength of the → calcium break, as measured from the fluxes in the intervals 3750-3950 Å and 4050-4250 Å. It is given by the expression Ca-break[%] = 100 · (f_upper - f_lower)/f_upper,
where f_upper and f_lower are the mean fluxes measured in the 3750-3950 Å and 4050-4250 Å bands, respectively,
in the rest frame
(Dressler & Shectman 1987, AJ 94, 899).

See also: → calcium; → break; → index.

To perform a mathematical process; to reckon; to make an estimate of; evaluate. → compute; → count; → mathematics; → statistics.

Etymology (EN): Calculate, from L.L. calculare, calculat-, from L. calculus “small stone, pebble” (used in reckoning), dim. of calx, calc- “limestone,” from Gk. khalix “small pebble,” kakhlex “round pebble,“cf. O.E. hægl, hagol “hale,”
from W.Gmc. *haglaz, O.H.G. hagal, O.N. hagl, Ger. Hagel “hail”, PIE *kaghlo- “pebble, hail.” The Pers. cognate is probably the Lori hogela “big stone.”

Etymology (PE): Afmârdan, from prefix af- + stem mar- + infinitive suffix -idan. The Mod.Pers. prefix af- “to, up, upon,” occurring in several words (e.g. afzudan, afruxtan, afsar, afsâr, afqân), derives from O.Pers./Av. abiy-/aiwi- “to, upon, against;” cf. Skt. abhi-, Gk. amphi-. The stem mar-, mâr- “count, reckon, measure,” which occurs in several Mid./Mod.Pers. terms (e.g. ošmârdan, šomârdan, šomordan “to count, to calculate,” âmâr “computation, arithmetic; statistics,” âmârdan “to reckon, to calculate,” bimar “countless,” nahmâr “great, large, big”), is related to the Av. base mar- “to have in mind, remember, recall,” hišmar-; cf.
Skt. smr-, smarati “to remember, he remembers,” L. memor, memoria, Gk. mermera “care,” martyr “witness.”

The act, process, or result of calculating.

Etymology (EN): Calculation, noun from → calculate.

Etymology (PE): Afmâreš, verbal noun from afmârdan→ calculate.

A small electronic device that performs calculations.

Etymology (EN): Calculator, from → calculate + → -tor.

Etymology (PE): Afmârgar, from afmâr→ calculate + -gar agent suffix, from kar-, kardan “to do, to make” (Mid.Pers. kardan, O.Pers./Av. kar- “to do, make, build,” Av. kərənaoiti “makes,” cf. Skt. kr- “to do, to make,” krnoti “makes,” karma “act, deed;” PIE base k^wer- “to do, to make”).

The branch of mathematics that deals with limits and the → differentiation and → integration of → functions of one or more → variables. Same as → infinitesimal calculus and → differential calculus .

Etymology (EN): L. calculus “small stone,” from calx, calcis “limestone,” → calculate, + -ulus diminutive suffix, → -ule.

Etymology (PE): Afmârik, from afmâr, → calculate

• Pers. suffix -ik denoting a subject, a branch of sciences, a discipline, → ics.

A → claculus based on the properties of the successive values of → variable quantities and their → differences or → increments.

Etymology (EN): → calculus, → finite, → difference.

Etymology (PE): Afmârik, → calculus, degarsânihâ, plural of degarsân, → difference, karânmand,
→ finite.

A branch of mathematics that deals with the calculation of the probabilities of events.

Etymology (EN): → calculus; → probability.

Etymology (PE): Afmârik, → calculus; šavânâihâ, plural of šavânâi→ probability.

The application of → Cauchy’s theorem to compute residues and poles, evaluate contour integrals, sum infinite series, and carry out related calculations.

See also: → calculus; → residue.

The branch of mathematics dealing with the differentiation of tensors.

Etymology (EN): → calculus; → tensor.

Etymology (PE): Afmârik, → calculus; → tensor.

The study of maximum and minimum properties of → definite integrals.

Etymology (EN): → calculus; → variation.

Etymology (PE): Afmârik, → calculus; varteš→ variation.

The area of calculus dealing with differentiation and integration of vector-valued functions; a sub-area of tensor calculus.

Etymology (EN): → calculus; → vector.

Etymology (PE): Afmârik, → calculus;
bordâr, → vector.

A large, roughly circular, → crater with diameter at least three or four times depth on the summit or in the side of a → volcano. A caldera can form from a volcanic blast or the collapse of a volcanic cone into an emptied → magma chamber.

Etymology (EN): From Sp. caldera “cauldron, kettle,” also name of a crater on Canary Islands, from L. caldarius “of warming,” from calidus “warm, hot,” → calorie.

Etymology (PE): Tiyân “large cauldron; cauldron used for warming water in a communal bathhouse,” of unknown origin.

A collection of 109 impressive celestial objects compiled for amateur astronomers. These objects (→ star clusters, → nebulae, → supernova remnants, and → galaxies), selected from the → New General Catalog and the → Index Catalog, are not present in the → Messier catalog.

See also: Named after Patrick Caldwell Moore (1923-2012), English amateur astronomer, who compiled the catalog in 1995; → catalog.

1. Any of various systems for measuring and recording the passage of time by dividing the year into days, weeks, and months.
   
2. A table showing the months, weeks, and days in at least one specific year.
   → chronology.

Etymology (EN): M.E. calender, from O.Fr. calendier, from L. calendarium “account book,” from kalendae “calends” the first day of the Roman month,
from calare “to announce solemnly, call out,” as the priests did in proclaiming the new moon that marked the calends, from PIE base *kele- “to call, shout” (cf. Skt. usakala “cock,” lit. “dawn-calling;” Gk. kaleo “to call,” kelados “noise,” kledon “report, fame;” O.H.G. halan, O.N. kalla “to call;” O.E. hlowan “to low;” Lith. kalba “language”).

Etymology (PE): Gâhšomâr, gâhšomâri, gâhmâr from gâh “time,” Mid.Pers. gâh, gâs,

• šomâr, mâr “reckoning,” → calculate.
  Sâlnâmé, from sâl, → year, + nâmé “a writing, letter, book.”

A period of 24 hours, from one midnight to the following midnight.

See also: → calendar; → day.

One of the periods into which a calendar is divided, ordinarily 12, but in earlier systems 10 (the first Roman calendar under Romulus) or 13 (ancient Iranian calendar using a month intercalation).

See also: → calendar; → month.

The time interval between the new year’s day in a given calendar system and the day before the following new year’s day. In the Gregorian system the calendar year begins on January 1 and ends on December 31. In the Iranian calendar it begins on Farvardin 1, the day closest to the spring equinox and ends on Esfand 29 or 30.

See also: → calendar; → year.

1. Young of a bovine animal. See also → calve, → glacier calving.
   

   2. The fleshy part of a person’s → leg below the → knee.

Etymology (EN): M.E., from O.E. cealf, calf, cognate with M.Du. calf, Ger. Kalb, Gothic kalbo.

Etymology (PE): 1) Gug (Dehxodâ), variant gog “calf;” probably from Proto-Ir. *gao-ka “baby cow, little caow,” from *gao- “cow, bull,” → cow, + suffix -*ak.
Gusâlé, literally “young in years,” from gu, → cow, + sâl, → year.

2. Poviz, from Laki poviz “calf,” may be ultimately from *povik, from *pov variant of pâ “leg, → foot” + suffix-ik, → -ics; cf. Ilâmi, Nahâvandi piz “the leg calf.”

To adjust or determine, by comparison with a standard, the response magnitude of a measuring instrument as a function of the input signal. For example, to determine line wavelengths in the spectrum of an astronomical object, or to graduate a hygrometer.

Etymology (EN): From M.Fr. calibre, via Sp. or It., from Ar. qalib “a mold, last,” perhaps from Gk. kalopodion “a shoemaker’s last,” from kalon “wood” + podos gen. of pous “foot.”

Etymology (PE): Kabizidan, verbal form of kabiz (varianats kaviz, kaviž, kafiz) “a measure for grain, a bushel,” from Mid.Pers. kabiz “a grain measure,” loaned in Arm. kapic “a grain measure,” and in Gk. kapithe, as attested in Xenophon.

1. The act or process of calibrating or the state of being calibrated.
   
2. A set of graduations that show positions or values.

Etymology (EN): Calibration, noun from → calibrate.

Etymology (PE): Kabizeš, noun from kabizidan, → calibrate.

An empirical curve obtained through appropriate exposures in order to determine the instrument’s response. For example, a curve allowing the conversion of relative intensities of an observed object into absolute fluxes, or a curve relating the detector’s pixel positions to wavelengths.

See also: → calibration; → curve.

A systematic error in the constant values to be applied to a measuring instrument.

Etymology (EN): → calibration; → error.

Etymology (PE): Irang, → error;
kabizeš, → calibration.

An exposure obtained with an instrument mounted on the telescope using an artificial illuminating source in order to calibrate the instrument.

Etymology (EN): → calibration; → exposure.

Etymology (PE): Nurdâd, → exposure; kabizeš, → calibration.

A lamp used for instrument calibration, such as an internal He-Ar arc for wavelength calibration or an external source of light placed in the telescope dome for flat-field exposures.

Etymology (EN): → calibration; lamp, from O.Fr. lampe, L. lampas, from Gk. lampas “torch, lamp, light, meteor,” from lampein “to shine.”

Etymology (PE): Kabizeš, → calibration; lâmp, from Fr., as above.

A general term for certain reference astronomical sources that allow determining the characteristics (magnitude, distance, velocity, etc.) of other sources. → primary calibrators, → secondary calibrators.

Etymology (EN): Calibrator, from → calibrate + → -or.

Etymology (PE): Kabizandé, agent noun from kabizidan, → calibrate.

1a) To cry out in a loud voice; shout.

1b) To command or request to come; summon.

1c) To speak loudly, as to attract attention; shout; cry.

2) To name or address (someone) as.  <BR>

3a) A cry or shout.

3b) The cry or vocal sound of a bird or other animal (Dictionary.com)

Etymology (EN): M.E. callen, from O.Norse kalla “to call out,” cognate with M.Du. kallen “to talk,” O.H.G. kallon “to shout,” akin to O.E. -calla “herald,” Irish gall “swan,” O.C.S. glasu “voice”.

Etymology (PE): Žâridan, from žâr, from Oroshori (or Roshorvi) žâr-/žart- “to sound, ring,” cognate with Parachi jâr “to say,” Ossetic gær, qær “noise, shout,” other cognates in Per. âžir “cry, call”, qâl, qil “noise, brouhaha,” jâr “cry, call”, žaqâr, zaqâr “cry, call”, payqâre “blame, reproval,” gerâmi “dear, beloved,” ultimately from Proto-Ir. *uz-garH-, from *garH- “to call, greet,” which has also given rise to Av. âγar- “to greet,” akin to Skt. garⁱ “to praise, welcome;” L. gratis “welcome;” PIE root g^werH- “to praise, to say.”

A period of 76 years after which the new and full moons would return to the same day of the solar year. This was intended as an improvement of the → Metonic cycle because the 6940 days of the Metonic cycle exceeded 19 years by about a quarter of a day, and exceeded 235 → lunations by a larger amount of time.

See also: Named after Calippus of Cyzicus (about 370-300 BC), a Greek astronomer and mathematician.

The eighth of → Jupiter’s known moons and the second brightest and the outermost of the four → Galilean satellites. With a diameter of 4800 km (0.38 Earths), Castillo is roughly the same size as Mercury. It orbits Jupiter in 16.689 days at a distance of 1,883,000 km from the planet, beyond Jupiter’s main → radiation belts. It is the third largest moon in the entire solar system. Its mass is 10.76 × 10²² kg (about 1.5 Earth Moons) and its mean → surface temperature is -155 °C. The most prominent feature of Callisto is its craters, as it has the most craters of any object in the solar system. Due to its orbit being further away from Jupiter, it is not under the same → tidal heating influences as → Io, → Europa, or → Ganymede.

Callisto’s thin → atmosphere is composed of → carbon dioxide and likely some → molecular oxygen. Callisto is thought to have formed as a result of slow → accretion from the → protoplanetary disk of gas and dust that surrounded Jupiter after its formation.

Etymology (EN): Callisto, an attendant of Artemis in Greek mythology. Because of her love affair with Zeus, she was transformed into a bear by Artemis. According to another legend she was changed into a bear by the jealous Hera. Zeus transferred her to the heavens as the → constellation  → Ursa Major (great bear).

1. Thermodynamics: The amount of → heat, in the → CGS system, required to raise the temperature of one gram of water from 14.5 °C to 15.5 °C at standard pressure. It is equal
   to 4.1858 → joules, a quantity called the 15° calorie. Also called gram-calorie, small calorie.
   

2. Physiology: A unit used to express the heat output of an organism and the fuel or energy value of food. It is equal to one kilocalorie.

See also: From Fr. calorie, from L. calor “heat,” calidus “warm;” PIE base *kelə- “cold; warm;”
Av. sarəta- “cold;” Mod.Pers. sard “cold, cool;” Skt. śiśira- “cold;”
Ossetian sald “cold,” Lith. šaltas “cold,”
silti “become warm;” Welsh clyd “cool.”

The measurement of the amount of → heat involved in various processes, such as chemical reactions, changes of state, and formation of solutions.

Etymology (EN): From L. calori- “heat,” combining form of calor, → calorie, + → -metry.

Etymology (PE): Garmâsanji, from garmâ  → heat

• -sanji  → -metry.

1. To give birth to a calf.
   

   2. Of a → glacier, to break off
      so as to give birth to an → iceberg. → glacier calving.

Etymology (EN): M.E. calven, O.E. (Anglian) *calfian, from → calf.

Etymology (PE): Gugidan, infinitive from gug “cow, bull,” → cow.

A satellite of Saturn discovered in 1980 on the images taken by Voyager 1. It shares the same orbit as Telesto and Tethys at a distance of 294,660 km and turns around the planet with a period of 1.888 days. It is 34 x 22 x 22 km in size.

Etymology (EN): In Greek mythology, Calypso was a sea nymph and the daughter of the Titan Atlas.

The Giraffe. An extended but inconspicuous
→ constellation near the north celestial pole. Approximate position: R.A. 5 h, Dec. 70°; abbreviation Cam, genitive form Camelopardalis.

Etymology (EN): M.E., from Medieval L. camlopardus, from L. camelopardalis, from Gk. kamelopardalis, from kamelos “camel” + pardalis, pard “leopard” (because the giraffe has a head like a camel’s and the spots of a leopard), from L. pardus, from Gk. pardos “male panther,” from the same source (probably Iranian) as Skt. prdaku- “leopard, tiger, snake,” and Pers. palang “panther.”

Etymology (PE): Zarrâfé “giraffe,” from Ar. zarafa, probably from an African language. This term is at the origin of
this animal’s name in European languages, via
It. giraffa. The Pers. name of the animal is: šotor-gâv-palang, from Mid.Pers., composed of šotor “camel” + gâv “ox, bull, cow,” → Taurus, + palang “panther.”

1. An apparatus for recording the light from an object onto a sensitive material, such as film or CCD detector.
   
2. A device that converts optical images into electrical impulses.

Etymology (EN): Mod.L. camera obscura “dark chamber” from L. camera “vaulted room,” from Gk. kamara “vault,” cf. Av. kamarâ- “waist; vault” Mod.Pers. kamar “waist,” Skt. kamarati “is vaulted;” PIE base *kam- “to arch.”

Etymology (PE): Kadak “small room,” from kad, kadé “room, chamber, habitation, vault, cell, cavern,” Mid.Pers. katak, Av. kata- “(small) room, closet, (small) house,” cf. Goth. hethjo “small room” O.S. kotici “cavern, nest,” PIE *kot(os).

A 3.6 m optical/infrared telescope jointly owned and operated by the Canadian National Research Council (NRC), the French Centre National de la Recherche Scientifique (CNRS), and the University of Hawaii. It became operational in 1979. The observatory is located atop the summit of Mauna Kea, a 4200 m, dormant volcano located on the island of Hawaii.

The Observatory headquarters is located in Waimea (also known as Kamuela by the US Postal Service).

Situated at the low latitude of Hawaii (+19° 45’), there is a fairly large sky overlapping with that of the → European Southern Observatory (ESO)  → La Silla observatory (δ = -29° 15’).

The point where an object is seen at the same → zenith distance from La Silla and from Mauna Kea, when it crosses the meridian, is δ =-5°. Taking into consideration also the difference in elevation between the observatories, the → declination at which one has equal air mass is moved down to δ =-18°. The extreme limit of observing from Mauna Kea is -60° (10° above horizon) but all programs below -20° are most efficiently carried out from ESO.

See also: Canada, from the St. Lawrence Iroquoian word kanata, meaning “village” or “settlement;”

France, from the L. Francia “country of the Franks;”

Hawaii, named for Hawai’iloa, a legendary figure from Hawaiian mytholgy;

→ telescope.

To make void; revoke; annul.

Etymology (EN): M.E. cancellen, from M.L. cancellare “to cross out,” from L.
cancellare “to make like a lattice,”
from cancelli “lattice, grating.”

Etymology (PE): Fâtaridan, from Sogd. fâtar “to remove, to set aside,” from *fra-taraya-, from *tar- “to cross” (Cheung 2007),
→ trans-.

The Crab. The dimmest → constellation of the → Zodiac, located in the northern hemisphere at approximately R.A. 8 h and Dec. +20°. The main feature of the constellation is the open cluster → Praesepe (M 44). Abbreviation: Cnc; genitive form: Cancri.

Etymology (EN): Cancer,from L., from Gk. karkinos; PIE base *qarq- “to be hard” (like the shell of a crab); cf. Skt. karkatah “crab,” karkarah “hard."
In Gk. mythology the Crab was sent by the goddess Hera to bite Hercules in the midst of the struggle with → Hydra, but Hercules crushed the crustacean
with his heel. Hera rewarded the Crab by placing it in the → Zodiac.

Etymology (PE): Xarcang “crab,” from Mid.Pers. karcang, cf. Lori qerženg from kar-, qer- + cang, ženg “claw.” The component
xar/qer may be related to Av. xruta-, xraoždva- “hard,” as in xruždisma- “hard ground” (from xruždi-

• zam-), and to the PIE *qarq- “to be hard.” In that case, the Pers. term for crab would literally mean “hard claw.”

→ Tropic of Cancer.

The → SI unit of → luminous intensity in a given direction; symbol cd. It is defined by taking the fixed numerical value of the → luminous efficacy of → monochromatic radiation of → frequency 540 × 10¹² Hz, K_cd, to be 683 when expressed in the unit lm W^-1, which is equal to cd sr W^-1, or cd sr kg^-1 m^-2 s³, where the kilogram, meter and second are defined in terms of → Planck’s constant (h), → velocity of light (c), and Δν_Cs.

See also: From L. candela, → candle.

1. An applicant or suitable person for a position.
   

2. An astronomical entity which is being considered for belonging to a special class of entities; e.g. → black hole candidate, → dark matter candidate, → supernova candidate.

Etymology (EN): From L. candidatus “clothed in white” (reference to the white togas worn by those seeking office),
from candidus “shining white,” from candere “to shine,” cf. Skt. cand- “to shine,” candra “bright; the Moon;”
PIE base *kand- “to glow, to shine.”

Etymology (PE): Nâmzad, literally “nominated,” from nâm, → name,

• zad, p.p. of zadan “to strike” (Mid.Pers. zatan, žatan, O.Pers./Av. jan-, gan- “to strike, hit, smite, kill,”
  Skt. han- “to strike, beat,”
  Gk. theinein “to strike,” L. fendere “to strike, push,” Gmc *gundjo “war, battle;” PIE *g^when- “to strike, kill”).

1. A cylinder or block of wax, tallow, or other fatty substance with a central wick, which is burned to produce light.
   

2. A unit of luminous intensity, superseded by the → candela.

Etymology (EN): M.E., O.E. candel, from L. candela “a light, torch,” from candere “to shine,” candidus “shining white” (E. candidate); cf. Skt. cand- “to shine, to glow,” candati “shines,” candra- “shining, glowing, the Moon;” Gk. kandaros “coal;” PIE base *kand- “to glow, to shine.”

Etymology (PE): Šam’, loan from Ar.

The Hunting Dogs. A small → constellation in the northern hemisphere at approximate position: R.A. 7h, Dec. +40°. Abbreviation: CVn, genitive form: Canum Venaticorum.

Etymology (EN): L. Canes Venatic from canes, pl. of canis “dog” + venatici, pl. of venaticus “hunting.” The constellation was created by the Polish astronomer Johannes Hevelius in his sky chart of 1687.

Etymology (PE): Tâzi “greyhound, hunting dog,” originally “swift, fast,” from tâzidan, tâxtan “to run, to assault, to chase,” Av. tak- “to run,” Skt. talki “he rushes at,” O.S. techim “to run away,” Lith. teku “to run, flow.” Sagân-e Tâzi, from sagân pl. of sag “dog” → Canis Major + tâzi.

The Greater Dog. A → constellation in the southern hemisphere which contains → Sirius, the brightest star of the whole sky. Approximate position: R.A. 7 h, Dec. -20°; abbreviation CMa; genitive form Canis Majoris.

Etymology (EN): L. Canis Major, from canis “dog” (cf. Gk. kuon, Skt. svâ-, Av. spâ-, Pers. sag; PIE *kwon-) + Maior “larger,” from L. major, irregular comp. of magnus “large, great” (cf. Gk. megas, Av. maz-, masan-, mazant- “great, important,” Skt. mah-, mahant-, Mod.Pers. meh; PIE *meg- “great”).
Canis Major is usually seen as one of the two hunting dogs of the hunter Orion. The other dog is Canis Minor, the Little Dog.

Etymology (PE): Sag-e Bozorg, from sag, see the above paragraph, + bozorg “large, great,” Mid.Pers. vuzurg, O.Pers. vazarka- “great,” Av. vazra- “club,” Skt. vajati, vaja- “strength,” vajra- “Indira’s thunderbolt,” L. vegere “to be lively,” PIE *weg- “to be strong, be lively.”

The Lesser Dog. A small → constellation in the equatorial region of the northern sky at approximately R.A. 7h 30m, Dec. +5°. It hosts the bright star → Procyon. Abbreviation CMi, genitive form Canis Minoris.

Etymology (EN): Canis Minor, from canis “dog” → Canis Major; L. minor “lesser, smaller,” from PIE base *min- “small” (cf. Gk. meion “less, lesser,” Skt. mi-, minati “to diminish.”

Etymology (PE): Sag “dog,” → Canis Major; kucak “small,” from Mid.Pers. kok, kotak, kotah “small, short; child.”

Canon of Eclipses. The most famous catalogue of solar and lunar eclipses. Published in 1887 by Theodor von Oppolzer, the catalogue contains the elements of all solar and lunar eclipses between 1208 BC and 2161 AD. It has been superseded by the calculations of F. Espenak and J. Meeus, Five Millennium Canon of Solar Eclipses: -1999 to +3000 (NASA/TP-2006-214141) and Five Millennium Canon of Lunar Eclipses: -1999 to +3000 (NASA/TP-2009-214172).

Etymology (EN): Canon, from L. canon, from Gk. kanon “a straight rod, a measuring rod, rule;” Ger. Finsternisse, plural from finsternis “eclipse; darkness,” from finster “dark,” M.H.G. vinster, O.H.G. finstar “dark” + -nis suffix forming abstract nouns, → -ness.

Etymology (PE): Fehrest “index, catalogue, canon,” → index; gerefthâ plural of gereft, → eclipse.

1. General: Pertaining to, established by, or conforming to a canon, i.e. a law or a general rule (especially in ecclesiastical matters).
   
2. Math.: Relating to the simplest or standard form of a general function, equation, rule, etc.

Etymology (EN): M.M. canonicalis, from canonic(us), from L. canon, from Gk. kanon “a straight rod, a measuring rod, rule " + alis, → -al.

Etymology (PE): Hanjârvâr, from hanjâr “a mason’s rule, any string or instrument used by builders in laying stones straight; rule, law, way, custom; a norm” + -vâr suffix meaning “having, endowed with; like, in the manner of.”

A periodic change in one of the components of the orbit of a celestial object.

See also: → canonical; → change.

Any set of generalized coordinates of a system together with their → conjugate momenta.

See also: → canonical; → coordinates.

The highest correlation between linear functions of two data sets
when specific restrictions are imposed upon them.

See also: → canonical; → correlation.

The most general form of an equation.

See also: → canonical; → equation.

The simplest expression of an equation, statement, or rule.

→ canonical; → form.

A two-component stellar → initial mass function with → slopes of 1.3 and 2.3 for massive and low mass stars, respectively. Also called universal IMF.

See also: → canonical; → IMF.

A model for the formation of the Moon according to which the → Moon results from a giant impact. A Mars-sized body (often referred to as → Theia) obliquely collided with the proto-Earth at the mutual escapee velocity. This specific giant impact is often used to represent all giant impacts. A recent advanced version of the canonical model is called → giant impact hypothesis.

See also: → canonical; → model.

Same as → conjugate momentum.

See also: → canonical; → momentum.

A physical upper mass limit near 150 Msun assumed for the stellar → initial mass function (Kroupa et al. 2012, arXiv:1112.3340).

See also: → canonical; → upper; → limit.

A generalized coordinate and its → conjugate momentum.

Etymology (EN): Canonically, adverb from → canonical; → conjugate; → variable.

The brightest star in the → constellation  → Carina and the second brightest star in the sky with a → visual magnitude -0.72. Also called α Carinae and HD45348. Canopus is not visible from latitudes above 37 degrees north. It is an evolved star, a → supergiant of type F0 II (Smiljanic et al., 2006, A&A 449, 655). Canopus lies 310 → light-years (96 → parsecs) from the Solar System; this is based on its → Hipparcos  → parallax measurement of 10.43 mas (5% accuracy). From this distance a → luminosity 13,300 times that the → solar luminosity is derived, and a radius of 73 times solar, in agreement with the → angular size (6.95 ± 0.15 mas) measured using → interferometry (Cruzalèbes et al., 2013, arXiv:1306.3288). These observations also yield an → effective temperature of about 7400 K. The star’s mass is estimated to be about 8 Msun. Canopus possesses an extremely hot magnetically heated → corona. Canopus’s corona is some 10 times hotter than the → solar corona and produces both observable → X-rays and → radio emission. According to calculations by J. Tomkin (1998, Sky & Telescope 95, 59), using → Hipparcos data, Canopus has, in the past, been the brightest star during three periods: from 3,700,000 to 1,370,000 years ago, from 950,000 to 420,000 years ago, and from 160,000 to 90,000 years ago. It will, once more, become the brightest star in 480,000 years and will remain such for 510,000 years.

Etymology (EN): Canopus, from Gk. kanobos, perhaps from Coptic language Kahi Nub “golden earth.”

Etymology (PE): Soheyl, from Ar. Suhail.
Agast, either a loan from Skt., or a possible, vanished Av. counterpart of Skt. Agasti, Agastya. The Skt. word derives from aga- “mountain,” and asti- “thrower.” In Vedic literature, Canopus is associated with the sage Agastya, one of the ancient rishis. The star is said to be the “cleanser of waters” because of turbid waters becoming clean at its rising.
Parak, of unknown etymology.

1. A covering for the head.
   

2. The top part of something (such as a hill or mountain). → polar cap.
   

3. A removable cover or lid.

Etymology (EN): M.E. cappe; O.E. cæppe “hood, head-covering,” from L.L. cappa “a cape, hooded cloak,” possibly shortened from capitulare “headdress,” from L. caput “head;” cf. Pers. Lori kapu “head,” kapulek “skull, middle of the head;” Kurd. Kurmanji qaf “head;” Pashto kaparay “skull;” Farâhâni kapâl “a blow on the head.”

Etymology (PE): Kolâhak, diminutive of kolâh “cap;” maybe related to PIE base *kel- “conceal;” cf. L. celare “to hide, conceal,” occulere “to dissimulate;” Gk. kalyptein “to cover,” kalia “hut, nest;” Skt. cala “hut, house;” Goth. hilms “helmet,” huljan “cover over,” hulistr “covering;” E. hull “seed covering,”
from O.E. hulu, from O.H.G. hulla, hulsa; O.E. hol “cave;”

The ratio of the charge Q on either conductor of a → capacitor to the → potential difference, or → voltage V between the conductors. It is given by C = Q/V. Capacitance can also be described by the relation:

C = ε₀A/d, where

ε₀ is the → permeability of free space, A is the area of one capacitor plate, and d is the distance between the capacitor plates. Capacitance is measured in → farads or, for convenience, in microfarads.

Etymology (EN): From capacit(y), → capacity + → -ance, a suffix used to form nouns either from adjectives in -ant or from verbs.

Etymology (PE): Gonjâyi, from gonjâ “able to hold,” from gonjidan→ capacity + -yi noun suffix.

A device for storing electric charge. The simplest sort of capacitors consists of two parallel, conductive plates having equal amounts of opposite charges and separated by a → dielectric material. When a capacitor is fully charged there is a → potential difference
between its plates. The larger the area of the plates and/or the smaller the separation between them the greater will be the charge that the capacitor can hold and the greater will be its → capacitance. The actual charge Q on the plates of a capacitor is given by: Q = C . V, where C is the capacitance and V the → voltage.

Etymology (EN): From capacit-, from → capacity + → -or.

Etymology (PE): From gonjân transitive stem of gonjidan “to be contained; to hold exactly; to be filled,” → capacity, + -gar, → -or.

The ability to receive or contain.
Electricity: → capacitance.

Etymology (EN): From M.Fr. capacité, from L. capacitatem, from capax “able to hold much,” from capere “to take, grasp.”

Etymology (PE): Gonjâyeš “capacity, holding, containing,” from gonjdan “to be contained; to hold exactly; to be filled;” Mid.Pers. winj- “to be contained;” Proto-Iranian *uiac-/*uic-; cf. Skt. vyac- “to contain, encompass,” vyás- “extent, content, extension;” L. uincire “to bind.”

The sixth brightest star in the sky, Capella lies in the Northern Hemisphere → constellation  → Auriga. Also known as HD 34029 = HR 1708 = HIP 24608.

Capella lies about 42 → light-years away (13.159 ± 0.015 → parsecs).

Its → apparent visual magnitude is V = 0.07. A → spectroscopic binary, it consists of a pair of G8 III and G0 III → giants with an → orbital period of 104 days.

The more evolved former/→ primary star has a slightly larger mass and luminosity (2.6 Msun and 79 Lsun) than that of the latter/→ secondary star (2.5 Msun and 73 Lsun). The primary is a typical late G giant presumably in the He-burning stage (→ red clump), which is lithium deficient and a slow rotator as other normal giants. In contrast, the secondary is a fast rotator (projected rotational velocity is v_e sin i ~ 35 km s-1) with high stellar activity (characterized by conspicuous chromospheric emission lines in UV) and shows a remarkably strong Li line, which indicates that the initial Li content is almost retained without being diluted (the surface Li composition for the secondary is ~100 times higher than that for the primary). That is, the secondary star belongs to the unusual group of Li-rich giants (see, e.g., Takeda et al., 2018, ApJ 862, 57 and Torres et al., 2015, ApJ 807, 26).

Etymology (EN): From L. capella “little she-goat,” diminutive of caper “goat.”

Etymology (PE): Bozbân “goat keeper” (Biruni, A.D. 973-1048, in his Tafhim), from boz, → goat, + -bân prefix denoting “keeper.”
Ayyuq, loan from Ar.

Same as → capillary action.

See also: → capillary; → -ity.

1. Resembling a strand of hair; hairlike.
   

2. Pertaining to or occurring in or as if in a tube of fine bore.
   

3. Physics: Pertaining to → capillarity.
   

4. Anatomy: One of the minute blood vessels between the terminations of the arteries and the beginnings of the veins (Dictionary.com).

Etymology (EN): From L. capillaris “pertaining to hair,” from capillus “hair.”

Etymology (PE): Muyin, muyiné, from mu(y), → hair.

The ability of a → liquid to → flow in a → narrow space, such as a thin → tube, without the assistance of, and in opposition to, external forces like → gravity. Also called → capillarity. It
occurs because of intermolecular → attractive forces between the liquid and solid surrounding surfaces. If the diameter of the tube is sufficiently small, then the combination of → surface tension (which is caused by → cohesion within the liquid) and → adhesion (between the liquid and the → container) acts to lift the liquid. The capillarity of the liquid is high when adhesion is greater than cohesion. For example, water in a thin glass tube has strong → adhesive forces due to the hydrogen bonds that form between the water molecules and the oxygen atoms in the glass wall (made of → silica, SiO₂). In contrast, mercury is characterized by stronger cohesion, and hence its capillarity is much lower.

See also: → capillary; → action.

→ Tropic of Capricorn.

See also: → Capricornus.

The Sea Goat. The smallest → constellation of the → Zodiac, lying in the Southern Hemisphere at approximately R.A. 21h, Dec. -20°.
Abbreviation Cap; genitive form Capricorni.

Etymology (EN): L. Capricornus “horned like a goat,” from caper “goat” + cornu “horn” (Gk. karnon, Skt. srnga-, Av. sru-, srvâ-, Mid.Pers. sruw, Mod.Pers. soru, P.Gmc. *khurnaz, Ger. Horn, E. horn, PIE *ker- “head, horn, top, summit”), a translation of Gk. Aigokheros, the name of the constellation.

Etymology (PE): Vahig, Mid.Pers. “goat,” the name of the Capricorn sign in Mid.Pers. texts, Mod.Pers. bahi, as mentioned by Biruni in his Athar al-Baqia written around A.D. 1000.

1. A title or explanation for a picture or illustration, especially in a magazine.
   

2. A heading or title, as of a chapter, article, or page (Dictionary.com).

Etymology (EN): M.E. capcio(u)n “taking, seizure,” from capcion “arrest, capture, imprisonment,” or directly from L. caption-, from capt(us) “taken,” → capture.

Etymology (PE): Kapéš “taking, capture,” verbal noun from kapidan
“to seize, take, capture,” related to qâpidan, qâp zadan “to rob, to seize,” Malâyeri qapâl “robbing, seizure, robbing,” probably related to L. capere, → capture.

The process in which an atomic, nuclear, or astronomical system acquires an additional particle or body.

Etymology (EN): From M.Fr. capture “a taking,” from L. captura “a taking,” from captus p.p. of capere “to take, hold, seize;” PIE base *kap- “to grasp” (cf. Skt. kapati “measure equal to the capacity of the hollows of the two hands joined;” Gk. kaptein “to swallow;” O.Ir. cacht “servant-girl,” literally “captive;” Goth. haban “have, hold;” O.E. habban, E. have “to have, hold;” probably Mod.Pers. qâp-, qâpidan, kapidan “to seize, rob”).

Etymology (PE): Gir-oft, composite verb from gir + oft. Gir “take, seize, hold,” from gereftan, from O.Pers./Av. grab- “to take, seize,”
cf. Skt. grah-, grabh- “to seize, take,” graha- “seizing, holding, perceiving,” M.L.G. grabben “to grab,” from P.Gmc. *grab, E. grab “to take or grasp suddenly;” PIE *ghrebh- “to seize.” Oft, from oftâtan “to fall; to befal, happen,” Mid.Pers. opastan, Av. pat- " to fly, fall, rush," Skt. patati “he flies, falls,” L. petere “to fall, rush out,” Gk. piptein “to fall,” PIE base *pet- “to fly, to rush.” Gir-andâzi, from gir + andâzi, verbal noun from gir-andâxtan “to throw, cast; to do, make.”

One of the first scientific hypotheses about the formation of the Moon, according to which the Moon formed elsewhere in the solar system and was pulled into a stable orbit by Earth’s gravity.

Observational facts do not confirm this hypothesis. For example, analysis of rocks from the Apollo landings confirm the Moon is made of similar material and rock as the Earth from about the same time and have almost identical oxygen isotopes in them.

Moreover, a captured moon, like Mars’ → Phobos and → Deimos do not have a spherical shape. See also → giant impact hypothesis, → fission theory, → co-formation theory.

See also: → capture; → theory.

A combining form used in the names of → chemical compounds in which → carbon is present. Also, especially before a vowel, carb-.

See also: From → carbon.

A molecular compound made from just three → chemical elements: → carbon, → hydrogen, and → oxygen. Carbohydrates have the general molecular formula C_xH_2yO_y, and thus were once thought to represent “hydrated carbon.” However, the arrangement of atoms in carbohydrates has little to do with → water molecules. Carbohydrates are a source of energy for the body. They include sugars, starches, cellulose and many other compounds found in living organisms. In their basic form, carbohydrates are simple sugars or monosaccharides.

See also: → carbo-; → hydrate.

Nonmetallic chemical element; symbol C. → Atomic number 6; → atomic weight 12.011; → melting point about 3,550°C; → boiling point 4,827°C. The most abundant isotope of carbon is ¹²C. Carbon is one of the most important elements for life. The burning of carbon in the form of coal and oils has been essential in the development of industrial societies. It is the element that hardens → steel and the sole element in → diamonds. The carbon in nature is produced inside massive stars. → triple-alpha process; → Hoyle state.

See also: Carbon, from Fr. carbone, coined by Antoine Lavoisier (1743-1794) to distinguish it from charbon (Fr.) “charcoal,” from L. carbo
(genitive carbonis) “a coal, charcoal.”

The stage in the evolution of a star after → helium burning when the core of the star consists mainly of carbon and oxygen. In stars of mass greater than about 8 solar masses, whose cores reach a temperature above 5 × 10⁸ K and density above 3 × 10⁹ kg m^-3, carbon burning can begin via reactions such as the following:
¹²C + ¹²C → ²⁰Ne + ⁴He
¹²C + ¹²C → ²³Na + p
¹²C + ¹²C → ²³Mg + n.
The time-scale for this phase of → nucleosynthesis is of order of five hundred years.

See also: → carbon; → burning.

A problem raised in the past by observations suggesting that the amount of carbon necessary for standard → dust models was larger than what actually observed for the → interstellar medium (ISM) (Snow & Witt 1995). The problem was especially acute for the → 2175 A bump in the ultraviolet part of the → extinction curve. The so-called “crisis” was finally solved by, on the one hand, revising downward the → solar abundances, thought to represent the ISM abundances (Asplund et al. 2009, arXiv:0909.0948, and references therein), and, on the other hand, revising upward the ISM carbon abundances (Sofia et al., 2011, AJ 141, 22S).

See also: → carbon; → crisis.

1. A complex series of processes through which all the carbon atoms on Earth is cycled through the air, ground, plants, animals, and fossil fuels. During the cycle, plants absorb → carbon dioxide (CO₂) from the atmosphere and through → photosynthesis incorporate the associated carbon atoms into sugars and other molecules necessary for growth. Plants return carbon atoms back to the atmosphere in the form of CO₂. However, much of the carbon absorbed remains “locked up” in the living organisms until decomposition or fire releases it back to the atmosphere.
   

2. For nuclear fusion in stars → CNO cycle.

See also: → carbon; → cycle.

CO₂, also called carbonic acid gas. A colorless gas which occurs in the atmosphere playing an essential part in animal respiration and the growth of green plants. → photosynthesis, → carbon cycle. It is formed by the → oxidation of carbon and carbon compounds. Carbon dioxide is the most important → greenhouse gas produced by human activities, primarily through the combustion of fossil fuels. Its concentration in the Earth’s atmosphere has risen by more than 30% since the Industrial Revolution. CO₂ forms a solid at -78.5 °C at atmospheric pressure, and is used as a refrigerant in this form as a dry ice for the preservation of frozen foods. As carbon dioxide gas is heavier than air and does not support combustion, it is used in fire extinguishers.
CO₂ is present in the → interstellar medium and is one of the main → molecules in → comets.

See also: → carbon; → dioxide.

A colorless, odorless, very poisonous gas which burns in air with a bright blue flame to form → carbon dioxide. CO gives rise to a violent explosion when ignited in air in certain proportions. It occurs in coal gas and in the exhaust fumes of motor engines. Melting point -207 °C; boiling point -191.1 °C.

Carbon monoxide is the most important → molecule found in the → interstellar medium, and is produced through several chemical reactions, → CO formation. It was discovered in 1970 by R. Wilson and A. Penzias of Bell Laboratories, using the 11-m telescope of the National Radio Astronomy Observatory (NRAO) in the direction of the → Orion nebula. Because the CO line is so intense and widely distributed in space, this molecule is a most useful tool for tracing the ISM. In addition, measurement of its rare isotopes have shown that the main line ¹²C¹⁶O (wavelength 2.6 mm, 115 GHz) is
→ optically thick, that is the → column density of the molecule is so high that the material becomes opaque at the transition frequency. Moreover, the upper-energy levels of the CO molecule are easily excited by collision with → molecular hydrogen. The combination of high → optical depth and the ease of → excitation imply that CO emission brightness will accurately reflect the local gas temperature. CO is also one of the principal molecules detected in → comet nuclei.

See also: → carbon; → mono-; → oxide.

A class of → red giant stars whose spectra show strong → molecular bands of → carbon compounds.

See also: → carbon; → star.

A radioactive isotope of carbon, whose nucleus contains 6 protons and 8 neutrons;
also called → radiocarbon. ¹⁴C is naturally produced in the atmosphere when a neutron created by a cosmic ray hits the nucleus of an atom of nitrogen-14. The nucleus absorbs the neutron and ejects a proton, thereby transforming itself into ¹⁴C. It decays back to nitrogen, with a half-life is 5730 years, after emitting an electron (¹⁴₆C → ¹⁴₇N + e^- + ν_e). See also → radiocarbon dating.

See also: → carbon; → four + -teen, an inflected form of the root of → ten.

A star that presents very low → iron  → abundances [Fe/H] < -4 but an → anomalous richness in carbon. CEMP stars have been defined as a subset of → metal-poor stars that exhibit elevated [C/Fe] ≥ +1.0. It has been recognized that ~15-20% of stars with [Fe/H] < -2.0 are carbon enhanced. This fraction rises to 30% for [Fe/H] < -3.0, to 40% for [Fe/H] < -3.5, and ~75% for [Fe/H] < -4.0. This increasing trend of CEMP-star frequency with declining [Fe/H] is confirmed by the observation of many thousands of CEMP stars (Daniela Carollo + ApJ 2014, 788, 180). See also → extremely metal-poor star (EMPS)

See also: → carbon; → enhance; → metal; → metal; → poor; → star.

Containing or composed of carbon.

Etymology (EN): From → carbon + -aceous, from L. -aceus “-ous.”

Etymology (PE): Karboni, adj. from karbon, → carbon; karbondâr “having carbon,” with -dâr “having, possessor,” from dâštan “to have, to possess;” O.Pers./Av. root dar- “to hold, keep back, maintain, keep in mind;” cf. Skt. dhr-, dharma- “law;” Gk. thronos “elevated seat, throne;” L. firmus “firm, stable;” Lith. daryti “to make;” PIE base *dher- “to hold, support.”

A rare type of → stony meteorite having a higher → carbon content than other classes of meteorite. They represent only ~5% of the known meteorites. Their bulk composition is mainly → silicates, → oxides and sulfides, whilst the minerals → olivine and serpentine are characteristic. The six classes of carbonaceous chondrites are: → CI chondrites, CM chondrites, CV chondrites, CO chondrites, CK chondrites, CR chondrites, CH chondrites, and CB chondrites.

See also: → carbonaceous; → chondrite.

The radical -C=O, which occurs in several compounds, such as → aldehydes and ketones.

See also: From → carbon + -yl a suffix used in the names of some radicals; → group.

Chem.: The -COOH group, regarded as the essential and characteristic constituent of organic acids.

See also: From carb-, variant of carbo- before a vowel, from → carbon, + ox, from → oxygen,

• -yl a suffix used in the names of radicals.

1. Fundamentally → important; → principal.
   

2. → cardinal number.

Etymology (EN): M.E., from L.L. cardinalis “principal, pivotal,” lit. “serving as a hinge,” from cardo, cardin- “door hinge.”

Etymology (PE): Agrâ, from Av. aγra-, aγrya- “the highest, the first, foremost” cf. Skt. agra- “foremost, first, prominent,” PIE *agro- “top, first, beginning.”

Any of the four principal directions or points of the compass, → north, → east, → south, and → west. See also: → cardinal point.

See also: → cardinal; → direction.

An ordinary number such as 0, 1, 2, or 3, as opposed to an → ordinal number such as 1st, 2nd, or 3rd. Cardinal numbers can be → zero or → positive
and are used for counting the things that are assumed to be not divisible.

See also: → cardinal; → number.

One of the four points where the → meridian and the → prime vertical intersect the → horizon. See also: → cardinal direction.

See also: → cardinal; → point.

Math.: The → cardinal number indicating the → number of → elements in a → set. For example, the set A = {a, b, c, d} contains 4 elements, and therefore it has a cardinality of 4 (denoted |A| = 4).

See also: → cardinal; → -ity.

1a) A state of mind in which one is troubled; worry, anxiety, or concern;
a cause or object of worry, anxiety, concern, etc.

1b) Serious attention; solicitude; heed; caution.

2a) To be concerned or solicitous; have thought or regard.

2b) To be concerned or have a special preference (Dictionary.com).

Etymology (EN): M.E., from O.E. caru, cearu “sorrow, anxiety, grief,” cognate with Gothic kara, O.H.G. chara lament; M.En. caren, O.E. cearian, carian “be anxious, grieve.”

Etymology (PE): Timâr “care, attendance on the sick; custody; sorrow;” Mid.Pers. têmâr “care; grief”

1. Cautious in one’s actions.
   

2. Taking pains in one’s work; exact; thorough.
   

3. (of things) Done or performed with accuracy or caution (Dictionary.com).

See also: → care; + -ful, a suffix meaning “characterized by; full of; able to;” → full.

The Keel. A major → constellation in the southern sky, home to → Canopus (α Carinae), the second brightest star after → Sirius. Approximate position: RA 9h, Dec. -60° The constellation resulted from the division of a very large constellation representing → Argo Navis, the mythological Jason’s ship. The partition into the
constellations → Carina, → Puppis, → Vela, and → Pyxis appeared first on a sky map by Nicholas Louis de Lacaille (1763). Carina represents the bottom of the Ship Argo. Abbreviation:
Car; genitive form: Carinae.

Etymology (EN): L. carina “the keel of a ship, i.e. the principal structural member of a ship, running lengthwise along the center line from bow to stern, to which the frames are attached.”

Etymology (PE): Afzal “keel” in the jargon of the Caspian sea fishermen
of Gilan province. Šâh-taxté “main plank.”

A → spiral arm in the Milky Way galaxy seen at its best in the → constellation → Carina, but also crossing the constellations → Vela,
→ Crux, and → Centaurus. It may be a continuation of the → Sagittarius arm; the combined feature is called Sagittarius-Carina arm.

See also: → Carina; → arm.

One of the most prominent → massive star formation regions of the → Milky Way, also known as NGC 3372. It is associated with a giant → H II region of the same name, which spans about 4 square degrees on the sky and is split by a remarkable V-shaped → dust lane. The Carina Nebula harbors several → star clusters, mainly
→ Trumpler 14, → Trumpler 16, and Collinder 228, including
more than 60 known → O-type stars in addition to the extreme → LBV star → Eta Carinae. This gas and dust complex is associated with a → giant molecular cloud extending over about 130 pc. Large cavities within the molecular cloud are supposed to be carved out by the massive star clusters. There are also several → Herbig-Haro objects and → bipolar outflows.

See also: → Carina; → nebula.

The fourteenth of Jupiter’s known satellites; 40 km in size; → retrograde orbit. It was discovered by Nicholson in 1938.

Etymology (EN): In Gk mythology, Carme was a wife of Zeus, and the mother of
Britomartis, a Cretan goddess.

An experiment devised to produce → interference patterns from a beam of helium atoms passing through two
adjacent apertures, as in → Young’s experiment.

See also: Named after O. Carnal and J. Mlynek, who first carried out this experiment in 1991 (Phys. Rev. Lett. 66, 2689); → experiment.

A → cyclic process comprising a sequence of → isothermal and → adiabatic expansions and compressions that bring a system back to its initial state.

See also: Nicolas Léonard Sadi Carnot (1796-1832), a French physicist and military engineer who, in his 1824 Reflections on the Motive Power of Fire, gave the first successful theoretical account of heat engines; → cycle.

1. An atom or molecule responsible for an unidentified spectral feature, such as a → diffuse interstellar band.
   

2. Same as → charge carrier.
   

3. In radio or television transmission, an → electromagnetic wave whose → amplitude, → frequency, or → phase is to be varied or → modulated to transmit a signal.

Etymology (EN): Carrier, from v. carry, from M.E. carien, from O. Norm-Fr. carier “to transport in a vehicle,” from carre “cart,” from L. carrum, carrus “two-wheeled wagon,” from Gaul. karros, from PIE *krsos, from base *kers- “to run.”

Etymology (PE): Barandé “carrier,” from bordan “to carry,” Mid.Pers. burdan, O.Pers./Av. bar- “to bear, carry,” Av. barəθre “to bear (infinitive),” barəθri “a female that bears (children), a mother,” Skt. bharati “he carries,” Gk. pherein, P.Gmc. *beranan, O.H.G. beran, Goth. bairan “to carry,” O.E. beran “bear, bring, wear,” PIE root *bher-; “to carry.”

A system for counting rotations of the Sun based on the mean → synodic rotation period of the Sun. Initially, Lord Carrington determined the solar rotation rate by watching low-latitude → sunspots. He defined a fixed solar coordinate system that rotates in a sidereal frame exactly once every 25.38 days. This means that the solar rotation period, as viewed from the Earth, is assumed to be constant. However, the synodic rotation rate varies during the year because of the changing speed of the Earth in its orbit and the mean synodic period is about 27.2753 days. Carrington rotation number 1 began on November 9, 1853.

See also: Named for Richard C. Harrington (1826-1875), British astronomer, who initiated the system; → rotation.

Of or relating to René → Descartes, his mathematical system, or his philosophy, especially with regard to its emphasis on logical analysis and its mechanistic interpretation of physical nature. → Cartesian coordinates; → Cartesian vortex theory.

See also: From L. Cartesianus, from Cartesius, Latinized form of the name of French philosopher and mathematician René Descartes (1596-1650), + suffix -ian.

A → coordinate system in which the position of a point is specified by two (in a plane) or three (in 3-dimensional space) → real numbers representing the distances from two perpendicular axes or from three perpendicular planes, respectively. René Descartes (1596-1650) introduced the coordinates system in his La Géométrie in 1637.

See also: → Cartesian; → coordinate.

A mechanical model put forward before Newton’s theory of gravity to explain the revolution of the planets around the Sun. Descartes in his 1644 Principia Philosophiae
postulated that the space between the Sun and the planets is filled with matter in the form of a fluid. The fluid rotates in countless whirlpools, one for each planet, thus carrying the planets along in their flow. The vortices vary in size and are contiguous as well as nested. Descartes believed that two objects can exert force on each other only when they are in physical contact. This is why he postulated that space is filled with matter. Newton refuted the vortex theory, using the principle of → action at a distance on which relies his → law of universal gravitation.

See also: → Cartesian; → vortex; → theory.

A galaxy with a striking ring-like feature lying about 400 million → light-years away in the → constellation  → Sculptor. The ring-like structure, over 100,000 light-years in diameter, is composed of regions of → star formation filled with very bright, → massive stars. The shape results from collision with another smaller galaxy.

Etymology (EN): Cartwheel, from cart from O.N. kartr;
→ wheel; → galaxy.

Etymology (PE): Kahkašân, → galaxy. Carx-e arrâbé “cartwheel,” from carx, → wheel

• arrâbé “cart, chariot,” maybe related to Mid.Pers. ras, ray “wheel,” O.Pers./Av. raθa- “wheel,” Khotanese rrha- “car,” Skt. ratha- “wheel,” L. rota “wheel,” PIE base *rotos “wheel.”

1. A waterfall or a succession of small waterfalls.
   
2. A succession of stages or processes, as in → cascade shower, → cascade error, → cascade transition.

Etymology (EN): From Fr., from It. cascata “waterfall,” from cascare “to fall,” from V.L. *casicare, from L. casum, p.p. of cadere “to fall,” → case.

Etymology (PE): Âbšâr, from âb “water,” → Aquarius, + šâr “pouring of water and liquids, waterfall;” peyšâr “waterfall succession,” from pey “step, succession,” as in peyâpey, + šâr. This word maybe related to Skt. sar- “to flow, run, hurry,” Gk. iallo “I send out,” L. salio “I jump.” It may also be variant of Mod.Pers. cal-, calidan “to walk, be going,” car-, caridan “to pasture, graze,” Av. car- “to come and go,” Skt. cari- “to move, walk, wander.”

An error that amplifies as the process of calculation goes on.

See also: → cascade; → error.

Multiple generations of secondary cosmic rays when the primary particles produce a succession of secondaries which have the same effects as the primary.

See also: → cascade; → shower.

A photon generation mechanism in an atom in which a transition initiates a series of secondary transitions from lower electronic levels.

See also: → cascade; → transition.

1. An instance of the occurrence, or existence of something.
   

2. A set of circumstances or conditions.
   

3. Grammar: An inflectional form of a noun, pronoun, or adjective indicating its grammatical relation to other words.

Etymology (EN): M.E. cas, from O.Fr. cas “an event, happening, situation,” from L. casus “a chance, occasion, opportunity; accident,” literally “a falling,” from cadere “to fall, sink, settle down” (Sp. caer, caida); Sp. caso; It. caso; Port. caso;
PIE root *kad- “to fall;” cf. Skt. śad- “to fall down;” Pers. kat, as below.

Etymology (PE): Kâté, from Iranian dialects/languages kat- “to fall” (with extension of the first vowel), as Laki: katen “to fall,” kat “he/she fell,” beko “fall!” (an insult); katyâ “fallen;” Lori: kat “event, error;” Kurd. (Soriani): kawtin “to fall, befall,” kett “fallen;” Kurd. (Kurmanji): da.ketin “to fall down;” Lârestâni: kata “to fall;” Garkuyeyi: darkat, varkat “he/she fell (sudden death);” Gilaki (Langarud, Tâleš): katan “to fall,” bakatam “I fell,” dakatan “to fall (in a marsh, in a pit),” vakatan “to fall from tiredness, be exhausted,” fakatan “to fall from (i.e., lose) reputation;” Tabari: dakətə “fallen,” dakətən “to crash down,” dakət.gu “stray cow;” Proto-Iranian *kat- “to fall;” cf. L. cadere, as above. Alternatively, from Proto-Ir. *kap-, *kaf- “to (be)fall, strike (down);” cf. Baluci kapag, kafag “to fall,” kapt “(past tense) fell;” Bampuri kapte “fallen;” Kurd. (Sanandaj) kaften “to fall;” Gilaki jekaftan “to fall;” Nâyini derkaftan “to fall down.”

A small attractive force that appears between two close parallel uncharged plates in a vacuum. It is due to quantum vacuum fluctuations of the electromagnetic field. According to the quantum theory, the vacuum contains → virtual particles which are in a continuous state of fluctuation. Because the distance between the plates is very small, not every possible wavelength can exist in the space between the two plates, quite in contrast to the surrounding vacuum. The energy density decreases as the plates are moved closer, creating a negative pressure which pulls the plates together. The first successfully measurement of the effect was by Steve Lamoreaux in 1997. A more recent experiment in 2002 used a polystyrene sphere 200 μm in diameter coated in gold or aluminium. This was brought to within 0.1 μm of a flat disk coated with the same metals. The resulting attraction between them was monitored by the deviation of a laser beam. The Casimir force was measured to within 1% of the expected theoretical value.

See also: After the Dutch physicist Hendrik Casimir (1909-2000), who predicted the phenomenon in 1948; → effect.

The main focus in → Cassegrain telescope.

See also: → Cassegrain telescope; → focus.

A reflecting telescope whose primary mirror has a hole bored through the center to allow the reflected light from the convex secondary mirror be focused beyond the back end of the tube.

Etymology (EN): Cassegrain, named after the French priest and school teacher Laurent Cassegrain (1629-1693), who invented this system in 1672;
→ telescope.

The main dark gap, 4,700 km wide, which divides Saturn’s outermost A and B rings.

See also: Named after Jean-Dominique Cassini (1625-1712), French astronomer of Italian origin, who discovered the division in 1675; → division.

A state characterizing a system which obeys → Cassini’s laws.

See also: → Cassini’s law; → state.

A joint endeavor of → NASA, → ESA, and the Italian space agency that sent a spacecraft to study the planet → Saturn and its system, including → Saturn’s rings and its natural satellites. The spacecraft was 6.70 m × 4 m × 4 m and weighed about 6 tons. Cassini drew its electric power from the heat generated by the decay of 33 kg of → plutonium-238. The spacecraft carried 12 sophisticated observation and measuring instruments. Cassini-Huygens was launched on 15 October 1997. It used several → gravity assist manoeuvres to boost itself toward Saturn. It flew past Venus two times (April 1998 and June 1999), made → flybys of Earth (August 1999), and f
Jupiter (December 2000). After 6 years and 8 months, covering about 8 billion km it entered Saturn orbit on July 1, 2004. It stayed there for 13 years and made detailed observations of the planet, its rings, and its moons.

A scientific probe called Huygens was released on December 25, 2004 from the main spacecraft to parachute through the atmosphere to the surface of Saturn’s largest and most interesting moon, → Titan.

The data that Huygens transmitted during its final descent and for 72 minutes from the surface included 350 pictures that showed a shoreline with erosion features and a river delta.

Cassini continued to orbit Saturn and complete many flybys of Saturn’s moons. A particularly exciting discovery during its mission was that of → geysers of water ice and organic molecules at the south pole of → Enceladus, which erupt from an underground global ocean that could be a possible environment for life. Cassini’s radar mapped much of Titan’s surface and found large lakes of liquid → methane. Cassini also discovered six new moons and two new rings of Saturn. The mission was ended on September 15, 2017 when the spacecraft was crashed into Saturn’s body and destroyed.

This was the best way to avoid contaminating Saturn’s moons with possible Earth microbes, because the moons may have the potential to support life.

See also: Named after two famous scientists. The Saturn orbiter is named after the Italian/french astronomer Jean-Domenique Cassini, who discovered the Saturnian satellites → Iapetus in 1671, → Rhea in 1672, and both → Tethys and → Dione in 1684. In 1675 he discovered what is known today as the → Cassini division, the narrow gap separating Saturn’s rings into two parts. The Titan probe was named Huygens in honor of the Dutch scientist, Christiaan Huygens, who discovered Titan in 1655.

Any of the three empirical laws governing the rotational dynamics of the → Moon:

1. The Moon rotates uniformly about its polar axis with a → rotational period equal to the mean → sidereal period of its orbit about the Earth.
   

2. The → inclination of the Moon’s equator to the → ecliptic is a constant angle approximately 1.5°.
   

3. The → ascending node of the lunar orbit on the ecliptic coincides with the → descending node of the lunar equator on the ecliptic. This law could also be expressed as: the spin axis and the normals to the ecliptic and orbit plane remain coplanar
   (Noyelles, 2009, Icarus, 202, 225).

See also: Named after Jean-Dominique Cassini (1625-1712), French astronomer of Italian origin, who established these laws in 1693 (Traité de l’origine et du progrès de l’astronomie), ; → law.

A prominent circumpolar → constellation in the northern sky. Its brightest stars form a distinctive, turning W shape. Abbreviation Cas, genitive form Cassiopeiae.

Etymology (EN): L. Cassiopea, from Gk. Kassiepeia, Andromeda’s mother and king Cepheus of Ethiopia’s wife, who boasted about her beauty to the degree that she considered herself more beautiful than the sea-nymphs. The consequences were awful for her daughter → Andromeda.

The second brightest star in the → constellation  → Gemini. This star has the identifier “alpha,” but it is fainter than β Geminorum (→ Pollux). Castor was known as a main sequence, blue star of magnitude 1.98 and → spectral type A1. However, it is actually a → gravitationally bound family of six stars.

The two brightest of the six, Castor A and Castor B, revolve around one another over a period of about 445 years. Castor A, the brighter of the two, is magnitude 1.9, while its companion is 3.0. Castor A is of spectral type A1 V and Castor B is Am. They are hotter than the Sun and about three times more massive, and lie 51 → light-years from Earth. Castor A and B are orbited by a third star called Castor C. It’s a 9th magnitude → red dwarf (dMe1) and lies about one arc minute to the south. Castor C is about 1,000 → astronomical units from the bright pair and takes 14,000 years to orbit around them.

Each of the three is a → spectroscopic binary making Castor a → sextuplet. Castor C is a → binary star of red dwarf stars a little more than half the size of the Sun. They revolve around one another evry 19 hours. The companions of Castor A and B are also smaller dwarf stars.

Etymology (EN): In Gk. mythology, Castor and → Pollux were twin heroes called the Dioscuri. Castor was the son of Leda and Tyndareus, Pollux the son of Leda and Zeus. They were great warriors and were noted for their devotion to each other. After Castor was killed by Lynceus, Pollux implored Zeus to allow his brother to share his immortality with him. Zeus created the constellation Gemini in their honor.

A prefix meaning “down,” also “against; back; by, about; with, along,” occurring originally  in loanwords from Greek; variants cat- and cath-, as in catalog, cataclysm, cataract, cathode, catastrophe, etc.

Etymology (EN): From Gk. kata-, before vowels kat-, from kata “down from, down to.”

Etymology (PE): Katâ-, kâtâ-, kât-, kat-, loan from Gk., as above.

1. A devastating flood; deluge.
   

2. Any violent upheaval that brings about great changes or causes great demolition. See also: → catastrophe.

Etymology (EN): From Fr. cataclysme, from L. cataclysmos “deluge,” from Gk. kataklysmos, from kataklyzein “to inundate,” from kata “down” + klyzein “to wash.”

Etymology (PE): Gatlur “great flood,” from gat “great, large, big” [Mo’in, Dehxodâ] + lur “flood” [Mo’in, Dehxodâ], cf. Gk. louein “to wash,” L. luere “to wash,”
Bret. laouer “trough,” PIE *lou- “to wash.” Variants of lur in Pers. dialects are: Lori, Kordi laf, lafow, lafaw, Tabari lé,
all meaning “flood.”

1. Of, pertaining to, or resulting from a → cataclysm.
   

2. Having the effect of, or of the nature of, a cataclysm. → cataclysmic variable.

See also: → cataclysm; → -ic.

A → variable star that shows a sudden and dramatic change in brightness, including → flare stars, → novae, and some types of → symbiotic stars. They are believed to be very → close binary systems consisting of an → accreting → white dwarf  → primary and an evolved → late-type secondary star that has filled its → Roche lobe. For systems with an → accretion disk, it is believed that a thermal instability
is the cause of repetitive outbursts observed in cataclysmic variables called → dwarf novae.

See also: → cataclysmic; → variable.

A list or record of items systematically arranged with descriptive details. → Index Catalogue; → Messier catalog; → New General Catalogue.

Etymology (EN): M.E. cathaloge, cateloge, from M.Fr. catalogue, from L.L. catalogus, from Gk. katalogos “a list, register,” from kata “down, completely” + legein “to say, count,” → -logy.

Etymology (PE): Kâtâlog, loan from Fr., as above.

Same as catalog position and
→ mean catalog place.

See also: → catalog; → place.

Same as catalog place and
→ mean catalog place.

See also: → catalog; → position.

A great, often sudden calamity; a complete failure; a sudden violent change in the earth’s surface. → cataclysm.

Etymology (EN): From Gk. katastrophe “an overturning, ruin,” from katastrephein “to overturn, ruin” from kata “down” + strephein “to turn.”

Etymology (PE): Negunzâr, from negun “overturned, inverted” + -zâr suffix denoting profusion, abundance, as in kârzâr “a field of battle; combat” šurezâr “unfertile, salty ground; nitrous earth,” xoškzâr “arid land,” and so forth.

The doctrine that certain vast geological changes in the Earth’s history were caused by sudden, short-lived, violent events rather than gradual evolutionary processes.

Catastrophism explains the differences in → fossil forms encountered in successive → stratigraphic levels. This doctrine is associated with the French naturalist Baron Georges Cuvier (1769-1832). Catastrohism is contrasted to the → uniformitarianism.

See also: → catastrophe; → -ism.

1. Unambiguously explicit and direct, without exceptions or conditions.
   

2. Relating to or included in a → category.
   

3. Logic: Of a → proposition (→ syllogism), consisting of a → subject and a → predicate, each of which denotes a class, and having one of the → Aristotelian forms.

See also: → category; → -ic; → -al.

In a → syllogism, a → proposition or statement that deals with inclusion or exclusion of members of → subject classes in → predicate classes. Categorical propositions are of four basic forms, see → Aristotelian form.

See also: → categorical; → proposition.

A standard → syllogism that consists of three → categorical propositions
in which there are three terms, and each term appears exactly twice. The three terms in a standard categorical syllogism are the → major term, → mino term, and → middle term.

See also: → categorical; → syllogism.

To place in a → category or class.

See also: → category; → -ize.

1. A group of things that are similar in some way.
   

2a) Philo.: In Aristotelian logic, any of the ten different ways
(substance, quantity, quality, relation, place, time, position, possession, doing, and undergoing) in which the subject of a proposition may relate to its predicate. For example, the proposition “All men are mortal” belongs to the Category of Quality since it tells us what “all men” are like, namely mortal.

2b) Philo.: In Kant’s system, any of the twelve (four groups of three each) pure concepts of the understanding that constitute necessary conditions of experience and correspond with the classes of judgements treated in formal logic. According to Kant, the categories are results of the mind’s activity, and are distinguished from sensation. The categories have, furthermore, like space and time relations, a peculiar universality. They are, in other words, a priori.

3. Math.: An entity consisting of a class of objects and a class of → morphisms between those objects that satisfy certain properties.

Etymology (EN): M.Fr. catégorie, from L.L. categoria, from Gk. kategoria, from kategorein “to speak against; to accuse, assert, predicate,” from kata “down, against, back,” → cata-,

• agorein “to speak before public assembly,” from agora “marketplace, public square” (from ageirein “to gather”);
  cognate with L. grex, gregis “herd, troop, crowd;” Skt. gramah- “heap, crowd, community;” Old Icelandic kremja “to squeeze;” O.E. crammian “to cram;” Latvian  gùrste “bundle of flask;” Polish garnac “to gather;” Russ. gorst’ “cupped hand;” cf. Pers. gor-, gal-, etc., as below; PIE base *ger- “to gather.”

Etymology (PE): Katâgor, from katâ-, → cata-,

• gor- “to gather,” ultimately from PIE *ger-, as above. We put forward that the following Iranian words derive from the above PIE base *ger- “to gather”:
  goruh “crowd, troop, band;”
  gallé (conversion of r to l) “herd, flock;”
  jarra (Laki) “group; stick bundle;”
  gerd in gerd âvardan “to collect, bring together” probably not related to gerd “round, circular;”
  xalam (štiyâni) “herd, flock;”
  xelima (Qâyeni) “herd;”
  korand, korang “a ring made by hunters or troops;”
  korka (Laki) “bundle of harvested ears of wheat;”
  gola, golé “bundle of hair; bunch”
  gola-gâh “place of gathering;”
  gurâb “market place in a village, agora;”
  

There are dozens of villages all-over Iran named Gorâb, Gurâb, Gela, Gola, Gala and their combinations with other words (e.g. Galadeh, Galazan, Galavand) that
probably refer to places of gathering.

One can also mention village names such as Agora, Gore, Gere(kalâ), Garaku, Oger, and so on in Mâzandarân;
Khotanese (prefixed ham-) gris “to assemble.”

A theory that deals with the concept of → category and
generalizes the → set theory.

See also: → category; → theory.

A negatively charged electrode that is the source of electrons in an electrical device.

Etymology (EN): Gk. kathodos “descent, a way down,” from kata- “down” + hodos “way, path.”

A kind of ray generated at the cathode in a vacuum tube, by the electrical discharge.

See also: → cathode; →ray.

Same as → universal astrolabe.

Etymology (EN): Catholic, M.E., from Fr. catholique, from Church Latin catholicus “universal, general,” from Gk. katholikos, from phrase kath’ holou “on the whole, in general,” from kata “about,” → cata-, + genitive of holos “whole,” → holo-; → astrolabe.

Etymology (PE): Ostorlâb, → astrolabe; hargâni, → universal.

Chemistry: A → positively charged → ion that is attracted to the → cathode in electrolysis. Any positively charged atom or group of atoms (opposed to → anion).

See also: From cat-, → cathod, + → ion.

Light that is reflected from a curved surface mirror.

See also: → catoprtics; → light.

An optical system in which the light is reflected only.

See also: → catoprtics; → system.

The area of → optics which treats of the laws and properties of light reflected from reflective surfaces.

Etymology (EN): From Gk. katoptrikos, from katoptron “mirror” (from kat-, → cata-, + op- “to see,” → optics, + -tron suffix of instruments) + -ikos, → -ics.

Etymology (PE): Bâztâbik, from bâztâb, → reflection, + -ik,
→ -ics.

Domesticated quadrupeds held on a farm, especially oxen, bulls, and cows.

Etymology (EN): M.E. catel, from M.Fr. catel “property” (O.Fr. chatel), from M.L. capitale “property, stock,” from L. capitalis “principal, chief,” literally “of the head,” from caput, → head.

Etymology (PE): Dâm, originally “nonferocious animal,” especially “herbivorous quadrupeds such as cows, sheep, etc.;” Mid.Pers. dâm “creature, creation;” O.Pers. dā- “to put, make, create;” Av. dā- “to place, put, create,”
dāmay- “creation; creating; creator,”
dāmi.dāt- “creating the creation;” cf. Skt. dhā- “to put, to place;” Gk. tithemi “to put, to place;” L. facere “to do;” O.H.G. tuon; E. to do.

A relationship between the → refractive index (n) and the wavelength of light (λ) passing through a medium. It is commonly stated in the following form: n = A + B/λ² + C/λ⁴, where A, B, and C are constants characterizing the medium. The two-component Cauchy equation is n = A + B/λ², from which the dispersion becomes dn/dλ = -2B/λ³ showing that dispersion varies approximately as the inverse cube of the wavelength. The dispersion at 4000 A will be about 8 times as large as at 8000 Å.

See also: Named after Augustin Louis Cauchy (1789-1857), French mathematician and physicist who found the first equation of dispersion in 1836; → equation.

If f(x) and φ(x) are two → continuous functions on the → interval [a,b] and → differentiable within it, and φ’(x) does not vanish anywhere inside the interval, there will be found, in [a,b], some point x = c, such that [f(b) - f(a)] / [φ(b) - φ(a)] = f’(c) / φ’(c).

See also: → Cauchy’s equation; → theorem.

Of, involving, or constituting a cause; indicative of or expressing a cause.

See also: Adj. from → cause.

In → special relativity, the causal relationship between → events involving a → light cone.

See also: → causal; → structure.

The relationship between causes and effects

Etymology (EN): Causality, from → causal + -ity.

Etymology (PE): Bonârmandi, from bonâr→ cause

• -mand suffix denoting relation, affinity + -i noun forming suffix.

The principle that cause must always precede effect.

See also: → causality; → principle.

1. The act or process of causing; the act or agency which produces an effect.
   

2. The relation of → cause to → effect.

See also: Verbal noun from → cause.

1. Effective or operating as a cause or agent.
   

2. Grammar: Expressing → causation; specifically, being a linguistic form that indicates that the subject causes an act to be performed or a condition to come into being (Merriam-Webster.com).

See also: Ultimately from L. causativus, → cause; → -ive.

1. A → reason for an → action or → condition; something that brings about an → effect or a → result.
   

2. To be the cause of; bring about.

Etymology (EN): From L. causa “reason, purpose,” of unknown origin.

Etymology (PE): Bonâr, from bon “basis, root, origin, ground”, from Mid.Pers. bun “base, root, origin;” Av. buna- “ground” (cf. Skt. budhna- “ground, bottom, depth”, L. fundus “bottom”, PIE base *bhud-/*bhund-) + âr short form of âvar present stem of âvardan “to cause or produce; to bring,” → production; compare with Ger. die Ursache “cause,” from ur- “primal” + die Sache “thing, matter.”

1. Capable of burning, corroding, or destroying living tissue. A caustic substance.
   

2. Optics: The enveloping surface formed by light rays reflecting or refracting from a curved surface. → caustic curve, → caustic surface.

Etymology (EN): M.E., from O.Fr. caustique, from L. causticus “burning,” from Gk. kaustikos “capable of burning,” from kaust(os) “combustible,” from kaiein “to burn” + -ikos, → -ic.

Etymology (PE): Sucân, from suc- “to burn,” variant of suz-, suzidan, suxtan “to burn;” cf. Baluci suc-, soc-;
Mid.Pers. sôxtan, sôzidan “to burn;” Av. base saoc- “to burn, inflame” sūcā “brilliance,” upa.suxta- “inflamed;” cf. Skt. śoc- “to light, glow, burn,” śocati “burns,” (caus.) socayati, śuc- “flame, glow,” śoka- “light, flame;” PIE base *(s)keuk- “to shine.”

The intersection of a → caustic surface with a plane passing through the beam of rays.

See also: → caustic; → curve.

In an → optical system, the → envelope of all the → reflected or → refracted rays
(by a → mirror or a → lens respectively) which do not come to a common focal point because of geometrical → aberration. This occurs when parallel rays of light fall on a → concave mirror or when a → convex lens
receives parallel light. In the case of → spherical aberration, the caustic surface has an axis of symmetry.

See also: → caustic; → surface.

The quality of being physically caustic.

See also: → caustic; → -ity.

1. An apparently hollow formation in the structure of an astronomical object, for example a sizable hole on the surface of a → molecular cloud created by → ultraviolet photons of a → massive star.
   

2. In a semiconductor laser, two reflective parallel edges forming a resonator that amplifies the light through stimulated emission.

Etymology (EN): From M.Fr. cavité, from L.L. cavitas “hollowness,” from L. cavus “hollow.”

Etymology (PE): Kâvâk, related to verb kâvidan (kâftan) “to dig; to examine, investigate,” cf. L. cavus “hollow” (E. derivatives: cavity, concave, cave,
excavate), Gk. koilos “hollow,” Armenian sor,
PIE *kowos “hollow.”

→ charge-coupled device.

See also: Short for → charge + coupled, from → couple, + → device.

A CCD detector having two dimensions.

See also: → CCD; → array.

→ charge-coupled device.

See also: → CCD; → detector.

One of a series of astronomical images obtained using a CCD detector in particular for calibration purposes.

See also: → CCD; → frame.

In a → CCD detector, the ratio of the initial number of electrons in a → pixel to the final number of → analog-to-digital units (or counts) reported by camera software. For example, a gain of 1.8 e-/count means that the camera produces 1 count for every 1.8 recorded electrons.

See also: → charge-coupled device (CCD); → gain.

A mechanical device of a CCD camera that controls the duration of a an exposure, as by opening and closing to allow the stellar light
to expose the CCD detector.

Etymology (EN): Shutter, from to shut, from O.E. scyttan from W.Gmc. *skutjanan + → -er.

A → cosmological model that attributes the formation of structures in the → early Universe to an exotic particle (→ cold dark matter) which was → non-relativistic at the time of → decoupling.
According to this model, CDM began clumping together soon
after the → Big Bang, while the → baryonic matter was still coupled with the → photons, and prevented to condense. Smaller → clumps of dark matter merged to form larger and larger clumps, and when the normal visible matter had decoupled from the photons, at the → recombination era (380,000 years after the Big Bang), it collapsed onto these dark matter clumps. In this way, the dark matter clumps acted as seeds for galaxy formation.

See also: → cold; → dark; → matter; → theory.

An often temporary cessation of hostilities during wartime for a specific purpose. It may be unilateral or bilateral.

Etymology (EN): From cease from O.Fr. cesser “to come to an end, stop,” from L. cessare “to cease, go slow, be idle,” + → fire.

Etymology (PE): Âtašbas, from âtaš, → fire,

• bas, from bas kardan “to stop, end; leave.”

Of or relating to the sky or visible heavens.

Etymology (EN): M.E., from O.Fr., from M.L. celestialis, from L. cælestis “heavenly,” from cælum “heaven, sky.”

Etymology (PE): Âsmâni related to âsmân, → sky.

The Earth’s axis extended to the → celestial pole.

See also: → celestial; → axis.

→ astronomical object.

See also: → celestial; → body.

Any system of coordinates used to define a point on the celestial sphere (zenith distance, altitude, celestial latitude, celestial longitude, etc.).

See also: → celestial; → coordinates.

An imaginary great circle on the sky half-way between the → celestial poles. It is the projection of the → equator of the Earth on the sky.

See also: → celestial; → equator.

A small globe representing the celestial sphere, on which the apparent positions of the stars are indicated.

See also: → celestial; → globe.

A great circle on the → celestial sphere having a plane that passes through the center of the Earth at a right angle to the line formed by an observer’s → zenith and → nadir.

See also: → celestial; → horizon.

Angular distance → north or → south measured from the → ecliptic to a → celestial object.

See also: → celestial; → latitude.

Angular distance to an object measured eastward along the → ecliptic from the → vernal equinox.

Etymology (EN): → celestial; → longitude.

Etymology (PE): Derežnâ, → longitude; âsmâni→ celestial.

The branch of astronomy that deals with the calculation of motions of celestial bodies under the action of their mutual gravitational attractions.

Etymology (EN): → celestial; → mechanics.

Etymology (PE): Mekânik, → mechanics; âsmâni,
→ celestial.

The great circle on the → celestial sphere, passing through the two → celestial poles and the observer’s → zenith.

See also: → celestial; → meridian.

→ astronomical object.

See also: → celestial; → object.

The point of the sky, north or south, where the projection of the Earth’s axis of rotation intersects the → celestial sphere. They are at 90° relative to the → celestial equator. Because of → precession, the celestial poles describe a circle around the ecliptic’s poles every 25,800 years.

See also: → celestial; → pole.

An imaginary sphere, of large but indefinite dimension, used as a basis to define the position coordinates of celestial bodies. The center can
be the Earth, the observer, or any other point which plays the role of origin for a given system of coordinates. Seen from the Earth, the celestial sphere rotates around the → celestial axis every 23h 56m 04s (the → sidereal day), as a result of the Earth’s rotation. Two important circles on the celestial sphere are the → celestial equator and the → ecliptic. The angle between them, about 23.40 degrees, is known as the → obliquity of the ecliptic. The celestial equator and the ecliptic intersect at two points, → vernal equinox
and → autumnal equinox. The positions of the → celestial poles and therefore that of the → celestial equator move gradually on the celestial sphere, due to → precession.

See also: → celestial; → sphere.

1. General: A small compartment or bounded area forming part of a whole.
   

2. Fluid mechanics: A body of fluid (air, liquid, or → plasma) in which the process of → convection proceeds.
   

3. Electricity: A device for producing electric current by chemical action.

Etymology (EN): From L. cella “small room, hut,” related to L. celare “to hide, conceal,” from PIE base *kel- “conceal” (cf. Skt. cala “hut, house,” Gk. kalia “hut, nest,” kalyptein “to cover”).

Etymology (PE): Yâxté “small room, closet,” etymology unknown.

The official name of the centigrade temperature scale with the → ice point as 0° and the → boiling point of water as 100°. The Celsius scale uses a degree (the unit of temperature) which has the same magnitude as the degree on the → Kelvin scale:
T_C = T_K - 273.15. See also → Fahrenheit scale, → Rankine scale, → Reaumur scale.

See also: In honor of Anders Celsius (1701-1744), Swedish astronomer, originator of the first centigrade temperature scale. However, in his original scale Celsius had 100° for the ice point and 0° for the steam point; → scale.

An → asteroid whose orbit around the Sun lies typically between the orbits of → Jupiter and → Neptune Neptune (5 to 30 → astronomical units). The first Centaur, called → Chiron, was discovered in 1977, but since then more than 100 roughly similar objects have been found. Three centaurs, Chiron, 60558 Echeclus, and 166P/NEAT 2001 T4, have been found to display → cometary  → comas. Chiron and 60558 Echeclus are now classified as both asteroids and → comets. Most of the Centaur asteroids are probably dormant comets from the → Kuiper belt which have been pulled in by the gravity of → outer planets.

See also: → Centaurus; → asteroid.

The Centaur. A → constellation in the southern hemisphere covering an extensive area of about 1060 square degrees from R.A. 11 h to 15 h and
Dec. -30° to -64°. Abbreviation: Cen, genitive form: Centauri.

Centaurus is the ninth largest constellation in the sky, but it does not contain any → Messier objects.

The brightest star in constellation is → Alpha Centauri which is also the third brightest star in the sky. Beta Centauri, the second brightest star in Centaurus, also called → Hadar, is the eleventh brightest star in night sky. Among other bright stars of the constellation are: Menkent (θ Cen), γ Cen, ε Cen, and η Cen. There are three → meteor showers associated with the constellation: the Alpha Centaurids, the Omicron Centaurids, and the Theta Centaurids. The constellation contains several extragalactic objects, among which: Centaurus A (NGC 5128), Omega Centauri, and NGC 5139.

Etymology (EN): L. centaurus, from Gk. kentauros, cf. Av. gandarəwa- “a mythical monster killed by Kərəsâspa,” Skt. gandharva- “name of mythical beings related with Soma.”
In Gk. mythology, centaurs were half-man half-horse creatures living on Mount Pelion in Thessaly, northern Greece. They were followers of the wine god Dionysus and well known for drunkenness and carrying off helpless young maidens.

Etymology (PE): Kentâwros, from Gk. “Kentauros.” Arabicized Qenturis (قنطورس).

The closest (3.8 ± 0.1 Mpc) → radio galaxy with a physical age of about 560 Myr, associated with the massive → elliptical galaxy NGC 5128. The nucleus harbours a → supermassive black hole, with a mass (5.5 ± 3.0) × 10⁷ Msol derived from stellar → kinematics. A prominent → dust lane, with → starburst, crosses the central parts. Centaurus A shows a twin → jet in → radio and → X-ray bands, symmetrical on
parsec scales but with evident asymmetry on kpc scales. The main (i.e. northern) jet which is markedly brighter than the counterjet, is seen at a viewing angle of approximately 50°. From photoionization models for such a viewing angle, the → Lorentz factor of the jet is derived to be ≤ 5. A large number of radio and X-ray → knots is discernible in the jet on kpc scales with the radio knots of larger proper motions showing comparatively little X-ray emission (see S. Wykes et al. 2015, MNRAS 447, 1005, and references therein).

See also: Situated in the → Centaurus constellation.

The nearest large → supercluster. It is dominated by the → galaxy cluster A3526 (→ Abell catalog). The Centaurus supercluster is a long structure that stretches away from us. The most distant of the clusters, A3581, is about 300 million → light-years away.

See also: → Centaurus; → cluster.

1. The point that is equidistant from all the points on a circle or sphere.
   

2a) To place in or on a center.

2b) Telescope: To move a telescope in order to place the object of interest on the center of the field. → center of attraction, → center of gravity, → center of inertia, → center of mass, → center wavelength, → anticenter, → apocenter, → barycenter, → optical center, → pericenter.

Etymology (EN): M.E. centre, from O.Fr. centre, from L. centrum “center,” originally fixed point of the two points of a compass, from Gk. kentron “sharp point, goad,” from kentein “stitch,” from PIE
*kent- “to prick.”

Etymology (PE): Markaz “center,” from Ar.;
kayân, Mod.Pers. “the point made by the compasses, that is the center of a circle” [Dehxodâ]; markazidan, infinitive from markaz, → center,

• -idan infinitive suffix.

A point toward which a force on a body is always directed.

See also: → center; → attraction.

A fixed point in a body through which the resultant force of gravitational attraction acts. Same as → center of mass, → center of inertia, → centroid.

Etymology (EN): → center; → gravity.

Etymology (PE): Gerânigâh, from gerâni→ gravity

• -gâh “place.”

Same as → center of gravity,
→ center of mass, → centroid.

See also: → center; → inertia.

Same as → center of gravity,
→ center of inertia, → centroid, and → barycenter.

See also: → center; → mass.

Center of a filter passband measured at 50% of peak transmittance.

See also: → center; → wavelength.

Prefix denoting one-hundredth of, in metric units; e.g. centimeter, 0.01 of meter.

Etymology (EN): Fr., from L. centi,- “hundred,” from centum “hundred,” Gk. hekaton, Av. satem-, Mod.Pers. sad, Skt. satam-, P.Gmc. *hunda- “hundred,” Goth. hund, O.H.G. hunt, O.Ir. cet, Bret. kant,
PIE *kmtom “hundred.”

Etymology (PE): Sânti-, from Fr., → above paragraph.

A unit of length in the → metric system, equal to one-hundredth of a meter, which is the current unit of length in the → International System of Units (SI).

See also: → centi-; → meter.

One of the three obscured → Galactic center clusters, which contains the supermassive black hole → Sgr A*. The first stars observed in the Central cluster were evolved → massive stars showing strong He I emission lines (2.058 microns) in the near infrared K band. Subsequently more than 80 massive stars were detected including various types of → Wolf-Rayet stars, as well as → O-type and → B-type → supergiants and → dwarfs (see, e.g. Martins et al. 2007, A&A 468, 233).

See also: → central; → cluster.

An eclipse during which the axis of the lunar shadow cone intersects the Earth’s surface (in the case of solar eclipses) or the axis of the terrestrial shadow cone intersects the Moon’s surface (in the case of lunar eclipses). The total and annular solar eclipses are usually central. They can also be not central; then, they are visible only from places situated at high latitudes (M.S.: SDE).

A → force that is always directed toward a fixed point and whose → magnitude depends only on the distance from that point.

Mathematically, F is a central force if and only if: F = f(r)r₁ = f(r)r/r, where r₁ = r/r is a unit → vector in the direction of r. If f(r) < 0 the force is said to be → attractive toward the source. If f(r) > 0 the force is said to be → repulsive from the source. In other words, a central force is one whose → potential, V(r), depends only on the → distance from the source. → Gravitational force and → electrostatic force are central, with V(r)∝ 1/r.

See also: → central; → force.

A statement about the characteristics of the sampling distribution of means of → random samples from a given → statistical population. For any set of independent, identically distributed random variables, X₁, X₂,…, X_n,
with a → mean μ and → variance σ², the distribution of the means is equal to the mean of the population from which the samples were drawn. Moreover, if the original population has a → normal distribution,
the sampling distribution of means will also be normal. If the original population is not normally distributed, the sampling distribution of means will increasingly approximate a normal distribution as sample size increases.

See also: → central; → limit; → theorem.

A vast, turbulent region encircling the → Milky Way’s nucleus that contains a large fraction of the → Galaxy’s dense → molecular clouds and → star formation regions. Spanning -1 to +1.5 degrees of → Sgr A*, the CMZ is about 400 pc × 100 pc in size and contains at least 10⁷→ solar masses of → giant molecular clouds,
approximately 10% of the Galaxy’s molecular gas. The gas in the CMZ is at higher temperature than typical giant molecular clouds
and has high velocity dispersion reflecting the → turbulent nature of the gas in the area.

Despite these extensive molecular reserves, the → star formation rate within the CMZ is actually lower than expected based on the analysis of nearby → star-forming regions in the quiescent → Galactic disk. A common assumption is that this is a result of the extreme conditions within the CMZ, where the density, pressure, temperature, → velocity dispersion and → radiation field are all significantly greater than elsewhere in the Milky Way (Clark et al. 2018, The Messenger 173, 22 and references therein).

See also: → central; → molecular; → zone.

The uplift of the central parts of the → crater floor due to the impacting force of a large → meteorite.

The shock wave entering the Earth will first move in as a compressional wave (P-wave), but after passage of the compressional wave an expansion wave (rarefaction wave) will move back toward the surface. This will cause the floor of the crater to be uplifted and may also cause the rock around the rim of the crater to bent upward.

See also: → central; → peak.

The primary component of a → computer that processes instructions. It runs the → operating system and → applications, constantly receiving input from the user or active → software programs. The CPU has two typical components:

1. Control Unit, which extracts instructions from memory and decodes and executes them.
2. Arithmetic Logic Unit (ALU), which handles arithmetic and logical operations.

See also: → central; → processing; → unit.

Same as → central peak.

Etymology (EN): → central; → up; → lift.

Etymology (PE): → central; → uplift.

1. In an interference filter, the wavelength of peak transmission.
   
2. In a spectrograph, the wavelength corresponding to the middle of the range covered by the grating or grism.

See also: Central, adj. from → center; → wavelength.

Acting or moving in a direction away from the axis of rotation or the center of a circle along which a body is moving.

Etymology (EN): From Mod.L., coined 1687 by Sir Isaac Newton from L. centri-,
combining form of centrum, → center, + fugere “to run away, flee.”

Etymology (PE): Markaz-goriz, from markaz,
→ center, + goriz “running away,” from gorixtan, gorizidan “to run away,” Mid.Pers. virextan, proto-Iranian *vi-raik, from vi- “apart, asunder”

• *raik, Av. raek- “to leave, set free, let off,” Mid./Mod.Pers. reg/rig (in mordé-rig “inheritance,” Skt. ric- “to leave,” rinakti “gives up, evacuates,” Gk. leipein “to leave,” L. linquere “to leave,” from PIE *linkw-, from
  *leikw- “to leave behind” (cf. Goth. leihvan, O.E. lænan “to lend;” O.H.G. lihan “to borrow;” O.N. lan “loan”).

Of a point rotating in a circle round a central point, the outward acceleration away from the rotation axis. It corresponds to → centrifugal force. The centrifugal acceleration is given by ω x ω x r, or v²/r, where ω is → angular velocity, r the distance to the rotating axis, and v the → tangential velocity. The centrifugal and → centripetal accelerations are equal and opposite.

See also: → centrifugal; → acceleration.

A force in a rotating reference frame directed outward from the axis of rotation.

See also: → centrifugal; → force.

Acting or moving toward a → center or → axis.
→ centripetal acceleration, → centripetal force.

Etymology (EN): From Mod.L., coined 1687 by Sir Isaac Newton from L. centri- combining form of centrum “center” + petere “to fall, rush out;” cf. Av. pat- " to fly, fall, rush," Skt. patati “he flies, falls,” Mid.Pers. patet “falls,” opastan “to fall,” Mod.Pers. oftâdan “to fall;” Gk. piptein “to fall,” petomai “I fly;” PIE base *pet- “to fly, to rush.”

Etymology (PE): Markaz-gerâ, from markaz, → center,

• gerâ “inclining,” from gerâyidan “to incline toward;” Mid.Pers. grâyitan, → diverge.

The rate of change of the → tangential velocity of a body moving along a circular path. The direction of centripetal acceleration is always inward along the → radius vector of the → circular motion. The magnitude of the centripetal acceleration is related to the → tangential velocity (v) and → angular velocity (ω) as follows: a_c = v²/r = rω². According to → Newton’s second law, an object undergoing centripetal acceleration is experiencing a → centripetal force.

See also: → centripetal; → acceleration.

The force exerted on an object in → circular motion which is directed toward the center and keeps the body in motion.
Centripetal force produces → centripetal acceleration, according to → Newton’s second law: F_c = ma_c. Its direction is always inward along the → radius vector, and its magnitude is given by: F_c= ma_c = mv_t²/r = mω²r.

See also: → centripetal; → force.

1. Same as → center of gravity, → center of inertia, → center of mass, and
   → barycenter.
   

2. In a triangle, the point where the three medians converge.

See also: → center + → -oid.

A class of luminous, → yellow supergiants that are pulsating
variables and whose period of variation is a function of their → luminosity.
These stars expand and contract at extremely regular periods, in the range 1-50 days.
Their highest brightness and surface temperature occur when their expansion velocity
is greatest. Similarly, their minima in brightness and temperature occur when they are in the contraction phase. The longer the period, the more luminous the star. The process that drives the pulsation of → Cepheid variables is the → kappa mechanism. In fact, Cepheids provide one of the most powerful tools for measuring distances to other galaxies (→ period-luminosity relation).
However, this method is limited to the distance of the → Virgo cluster of galaxies (15-20 → Mpc) even with the → HST or the largest ground-based telescopes. One particularly special Cepheid is the North Star, → Polaris. See also → RR Lyrae star.

Etymology (EN): Named after the prototype → Delta Cephei discovered by John Goodricke in 1784. → Cepheus.

A → variable star belonging to the class of → Cepheids.

See also: → Cepheid; → variable.

A → constellation in the Northern Hemisphere lying next to → Cassiopeia. It contains several pulsating variable stars, including the prototype → Cepheid variable Delta Cephei.
Abbreviation: Cep, genitive: Cephei.

Etymology (EN): In Gk. mythology, Cepheus, king of Ethiopia, who was married to the beautiful → Cassiopeia, and was also father of princess → Andromeda.

Etymology (PE): Kefeus, from Gk. Cepheus. Arabicizd form qifâvus (قیفاووس).

Once qualified as the largest known → asteroid, Ceres is now classified as a → dwarf planet (2006 IAU General Assembly). It is approximately 950 km across, and resides with tens of thousands of asteroids in the main → asteroid belt; it is the largest body of the belt. Its mass is 9.4 × 10²⁰ kg,
its → rotation period 9.074 hours, its → orbital period 4.60 years, and its → semi-major axis 2.767 AU.
NASA’s → Dawn spacecraft, which was placed in orbit around Ceres in 2015, has mapped its surface in great detail from a distance. Dawn caught sight of bright spots that soon resolved into more than 130 bright patches, most of them tied to craters. The most prominent of these spots lie inside the crater → Occator. The patches turned out to be carbonate salts, which only form in the presence of water. Since water skips to gas almost immediately on the dwarf planet’s surface, the discovery of carbonates suggested that there was liquid beneath the dwarf planet’s crust. Aside from craters, the only outstanding feature On Ceres is a single mountain, Ahuna Mons. It formed about 250 million years ago when plumes of saltwater and mud rose and erupted from within Ceres.

Etymology (EN): Ceres in Roman mythology was the goddess of growing plants and of motherly love. She was equivalent to Demeter in Gk. mythology.

European Organization for Nuclear Research, founded in 1954, and located on the Franco-Swiss border near Geneva, Switzerland. CERN is one of the world’s largest centres for scientific research. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter, i.e. the → elementary particles. The instruments used at CERN are particle → accelerators and → detectors. Currently it has 20 Member States.

See also: CERN, acronym of the organization’s original name Centre Européen pour la Recherche Nucléaire.

A complex of astronomical telescopes and instruments located approximately 80 km to the East of La Serena, Chile, at an altitude of 2,200 m. CTIO headquarters are located in La Serena, Chile, about 480 km north of Santiago. The principal telescopes on site are the 4-m Victor M. Blanco Telescope and the 4.1-m Southern Astrophysical Research (SOAR) telescope. One of the two 8-m telescopes comprising the Gemini Observatory is co-located with CTIO on the Association of Universities for Research in Astronomy (AURA) property in Chile, together with more than 10 other telescopes and astronomical projects.

See also: Cerro “mountain” in Spanish; Tololo a proper name; → inter-; American, from America, → North America Nebula; → Observatory.

Determined, fixed; established beyond doubt or question; indisputable. → determinism.

Etymology (EN): From O.Fr. certain, from V.L. *certanus, from L. certus “sure, fixed,” originally a variant p.p. of cernere “to distinguish, decide.”

Etymology (PE): Tâštig, from Mid.Pers. tâštig “certain,” tâšitan “to cut, cleave, create,” Mod.Pers. tarâšidan, Gilaki tâštan “to shave, scrape, cut,” Av. taš- “to cut, fashion, shape, form,” taša- “ax, hatchet,” tašan- “creator, maker,” cf. Skt. taks- “to cut, chop, form by cutting, make, create,” taksan “carpenter,” Gk. tekhne “art, skill, craft, method,” L. textere “to weave;” PIE base *tek- “to shape, make.”

The fact, quality, or state of being certain, especially on the basis of evidence. Something that is certain. → uncertainty; → uncertainty principle.

See also: Noun from → certain.

A soft ductile chemical element of the → alkali metal group;
symbol Cs. It is found in several → silicate minerals, including pollucite. The metal oxidizes in air and reacts violently with water. → Atomic number 55; → atomic weight 132.9054; → melting point 28.4°C; → boiling point 669.3°C; → specific gravity 1.873 at 20°C; and → valence +1. Cesium has several radioactive isotopes, among which ¹³⁴Cs
with a half-life of 2.07 years and ¹³⁷Cs with a half-life of 30.3 years. Cesium was discovered spectroscopically in 1860 by W. Bunsen and G. Kirchhoff in mineral water from Durkheim.

See also: From L. caesius “bluish gray,” which was the color of the cesium line in the spectroscope, + → -ium.

→ atomic fountain clock.

See also: → cesium; → clock.

The Whale, or Sea Monster. A large, rather inconspicuous → constellation in the equatorial region of the sky at R.A. 1h 30m, Dec. -10°. Its brightest star (Diphda) is a 2nd magnitude and contains → Mira Ceti, the first-known variable star, and the → Seyfert galaxy M77. Abbreviation: Cet; genitive form: Ceti.

Etymology (EN): Named after the sea monster in Gk. mythology sent by Poseidon to punish the Queen → Cassiopeia for bragging that she or her daughter → Andromeda was more beautiful than the Nereides. But → Perseus rescued Andromeda.

Etymology (PE): Ketus, from Gk., Arabicized form Qeytas (قیطس).

The system of → CGS units.

See also: → CGS unit; → system.

A → metric system of physical units based on → centimeter (length), → gram (mass), and → second (time).

See also: CGS, the initials of → centimeter,
→ gram, and → second; meter, kilogram, and second; → unit.

The first molecule detected in the interstellar medium. Methylidine radical (CH) was discovered by Walter S. Adams in 1937 using coudé spectroscopy in the direction of the bright star ζ Ophiuchi at the Mount Wilson Observatory (main CH line at 4300 Å).

See also: Chemical term based on Gk. methy “wine,” cognate with Pers. mey “wine,” from Mid.Pers. mad, may “wine;” Av. maδu- “wine, mead;” cf. Skt. mádhu- “honey, wine, sweet drink,” O.E. medu, E. mead, M.Du. mede, Ger. Met “mead;” O.C.S. medu, Lith. medus “honey;” Rus. m’od “honey,” m’édved’ “bear” (literally “honey-knower”); PIE base *médhu- “honey, sweet drink.”

→ CH (methylidine).

See also: → CH (methylidine); → molecule.

1. A series of usually metal links passing through one another, used for various purposes.
   

2. A series of things connected or following in succession. → chain reaction; → proton-proton chain.

Etymology (EN): Chain, from O.Fr. chaeine, from L. catena “fetter.”

Etymology (PE): Zanjir from Mid.Pers. zanjir “chain;” zanjiré, from zanjir + nuance suffix -é.

A succession of → nuclear fissions when the neutrons released by previous fissions produce other nuclear fissions
which themselves cause other reactions and the reactions goes on increasing exponentially.

See also: → chain; → reaction.

A high plateau site located at an altitude of 5,104 m in the Chilean Atacama desert, about 50 kilometers to the east of San Pedro de Atacama (longitude 67° 46’ W, latitude 23° 02’ S). It is the site of the → Atacama Large Millimeter Array.

See also: In Kunza, the ancestral language of the people living in the region, Chajnantor or Tchacknatur means “lift-off place.” It is the place of platforms for worshipping the Sun, where since immemorial time prayers and wishes lifted off (ESO book Cerca del Cielo).

A prefix meaning “copper,” used in the formation of compound words.

Etymology (EN): From Gk. chalko-, combining form of chalkos “copper.”

Etymology (PE): Xalco-, loan from Gk., as above.
Mes-, from mes, → copper.

→ chalcophile element.

See also: → chalco-; → -phile.

In the → Goldschmidt classification, a → chemical element that has an → affinity for sulphur, and therefore tending to be more abundant in sulphide minerals and ores than in other types of rock. This group is depleted in the silicate Earth and may be concentrated in the core. The group includes → silver (Ag), → arsenic (As), → bismuth (Bi), → cadmium (Cd), → copper (Cu), → mercury (Hg), → indium (In), → lead (Pb), → sulfur (S), → antimony (Sb), → selenium (Se), → tellurium (Te), and → thallium (Tl).

As a consequence of their relatively low

condensation temperatures (500-1100 K), most of these elements are depleted in terrestrial planets with respect to chondrites.

See also: → chalcophile; → element.

The Chameleon. A small inconspicuous → constellation in the southern hemisphere near → Crux, lying at approximate position: R.A. 11 h, Dec. -80°. Abbreviation: Cha; genitive form: Chamaeleonis;

Etymology (EN): From O.Fr. chaméléon, from L. chamaeleon, from Gk. khamaileon, from khamai “on the ground”
(akin to chthon “earth;” cf. Av. zam- “the earth,” Mid.Pers. zamig, Mod.Pers. zami, zamin “the earth,” Skt. ksam, L. homo “earthly being” and humus “the earth,” PIE *dh(e)ghom “earth”)

• leon “lion.”

Etymology (PE): Âftâbparast “chameleon,” literally “sun adorer,” from âftâb “Sun, sunlight” + parast “worshipper,”

An enclosed space making part of a laboratory apparatus, such as → bubble chamber, → cloud chamber, → multiwire proportional chamber.

Etymology (EN): M.E., from O.Fr. chambre, from L.L. camera “a chamber, room.”

Etymology (PE): Otâqak “small room, small chamber,” cf. Sogdian ôtâk “place, region,” ôtâkcik “local, regional, native” + -ak diminutive suffix.

Blowing out of → ionized gas from a → molecular cloud when the → ionization front of an → H II region created by an → embedded  → massive star arrives at the molecular cloud edge. The large → pressure gradient set up between the H II region and the → interstellar medium ejects the ionized material with velocities larger than 30 km/s, in a way comparable to champagne flowing out of a bottle.

Etymology (EN): From a hydrodynamical model first proposed by Guillermo Tenorio-Tagle (1979). Champagne, Fr., short for vin de Champagne “wine from Champagne,” a historical region at northeast France,
from L.L. campania “flat open country,” from L. campus “field;” → effect.

The flow of → ionized gas escaping from a → molecular cloud due to the
→ champagne effect.

See also: → flow.

Small-scale variations in the position of the Earth’s geographical poles within an irregular circle of 3 to 15 metres in diameter. It seems to result from two nearly circular components,
a seasonal variation in the mass distribution on the Earth (ice, snow, atmosphere) and movements of matter within the Earth.

See also: Named after Seth Carlo Chandler (1846-1913), the American astronomer who discovered the phenomenon; → wobble.

An astronomy satellite launched by NASA in 1999 July,
specially designed to detect X-ray emission from very hot regions of the Universe such as exploded stars, clusters of galaxies, and matter around black holes. Chandra carries a high resolution mirror (aperture 1.2 m, focal length 10 m), two imaging detectors (HRC and ACIS), and two sets of transmission grating spectrometer (LETG and HETG). Important Chandra features are: an order of magnitude improvement in spatial resolution, good sensitivity from 0.1 to 10 keV, and the capability for high spectral resolution observations over most of this range. Chandra was initially given an expected lifetime of 5 years, but on 4 September 2001 NASA extended its lifetime to 10 years “based on the observatory’s outstanding results.” Among the results obtained using Chandra one can mention the spectacular image of the → supernova remnant Cassiopeia A. See also → X-ray astronomy.

See also: Initially called Advanced X-ray Astrophysics Facility (AXAF), the satellite was
renamed the Chandra X-ray Observatory in honor of Subrahmanyan Chandrasekhar, the 1983 Nobel Prize in Physics, → Chandrasekhar limit.
Moreover, Chandra, or candra- means “moon” or “shining” in Skt., from cand- “to give light, shine;” cf. Gk. kandaros “coal;” L. candela “a light, torch,” from candere “to shine;” → X-ray; → Observatory.

A limiting mass of about 1.44 Solar masses that the theory predicts a non-rotating → white dwarf can attain without collapsing to become a → neutron star or a → black hole. Over this → critical mass, the degeneracy pressure will be unable to bear the load of the bulk mass.

Etymology (EN): Named after Subrahmayan Chandrasekhar (1910-1995), Indian-born American astrophysicist who, with William A. Fowler, won the 1983 Nobel Prize for Physics for his research on white dwarfs; → limit.

1. (v.intr.) To undergo change.
   

2a) (v.tr.) To → alter, modify, or make different; to make to pass from one state to another; to → exchange.

2b) To transform or convert.

3. To substitute another or others for; exchange for something else, usually of the same kind.
   

4. The act of changing; alteration or variation of any kind. → adiabatic change, → canonical change, → polytropic change, → secular change, → exchange.

Etymology (EN): M.E., from O.Fr. changier, from L.L. cambiare, from L. cambire “to exchange, barter,” of Celtic origin, cf. Breton kamm “curved, bent;” Gk. kampe “a corner, a joint;” L. campus “a field;”
Lith. kampus “corner;” PIE *kamb- “to bend, crook.”

Etymology (PE): Galnidan, variant of gardidan, gaštan “to change, to turn,” → Universe, cf. Awromani gelnây, geln- “to turn over” (Cheung 2007).

1a) General: A condition or place of great disorder or confusion.

1b) Math., Physics: Highly disordered evolution of some → dynamical systems
which is sensitively dependent on → initial conditions. In a → chaotic system
the → aperiodic, → nonlinear evolution grows → exponentially with time. Ordinary chaos is not → turbulence, but turbulence is always chaotic.

2. In → astrogeology, a distinctive area of fractured terrain on a planet or satellite, e.g. Gorgonum Chaos located in the southern hemisphere of Mars.

Etymology (EN): Chaos, in Gk. mythology and cosmology, the void existing at the beginning of the creation, as evoked in Hesiod’s (c. 850 B.C.) Theogony. However, the meaning of chaos, used by Hesiod, is a matter of debate. Some have interpreted it as the primeval absence of order (hence → confusion). Subsequently, the Roman writer Ovid (43 BC-17? AD) described Chaos in his Metamorphoses as an unordered and formless primordial mass, and opposed Chaos to Cosmos “the ordered universe.”

Chaos “gaping void,” from L. chaos, from Gk. khaos “abyss, that which gapes wide open, is vast and empty,” from *khnwos, from PIE base *gheu-, *gh(e)i- “to gape.”

Etymology (PE): 1) Varšun, from Tabari varâšun, Gilaki varâšin, daršin, uršin all meaning “confused, unordered, untidy,” cf. Qomi šur-o-šin “chaos, confusion”. The stem šun-/šin- is related to Mod.Pers. šân- in afšândan, šândan “to disperse, scatter, stew” (Mid.Pers. afšândan “to spread, scatter”), Gilaki šondan “to disperse,” Hamadani šuândan “to derange, disorder,” Laki veršânâ “to disperse, scatter,” Šuštari šayn “to shake, agitate,” Kermâni owšin “a winnowing fork to separate chaff from the grain,”
Laki šovâné “scattered household furniture,” Tabari timšan “sowing seeds;” all ultimately from Proto-Ir. *šan- “to shake;” see also → confuse. The prefix var-, variant bar- “up, over” (as well as dar- “in”), denotes “disorder, confusion” as in darham barham “upside-down, helter-skelter”.

2. Šivâr “depression between two terrains,” from Tabari; probably a variant of šiyâr, → groove.

The theory of unpredictable behavior that can arise in systems obeying deterministic scientific laws.

See also: → theory; → chaos.

Or, or relating to → chaos.

See also: Chaotic, adj. from → chaos.

The behavior of a → chaotic system.

See also: → chaotic; → behavior.

A system that is → deterministic through → description by mathematical rules but can evolve highly → nonlinearly depending on → initial conditions. See also
→ chaos.

See also: → chaotic; → system.

The condition of being → chaotic.

See also: → chaotic; → -ity.

In → dark energy models, a hypothetical fluid that can lead to cosmic acceleration at late times. In its simplest form, the Chaplygin gas has the → equation of statep = - A/ρ, where p and ρ denote the → pressure and → energy density, respectively, and A is a positive model parameter. This equation was introduced by Chaplygin (1904, Sci. Mem. Moscow Univ. Math., 21) to study the lifting force on a plane wing in aerodynamics.

See also: Named after Sergey Chaplygin (1869-1942), Russian physicist; → gas.

A band in the → absorption spectrum of → ozone (O₃) extending in the → visible from 400 nm to 700 nm. → Hartley band, → Huggins band.

See also: J. Chappuis, Acad. Sci., Paris, C. R. 91, 985 (1880).

1a) The aggregate of features and traits that form the individual nature of some person or thing.

1b) One such feature or trait; characteristic.

2. A person represented in a play, film, story, etc; role. See also
   → personage (Dictionary.com).
   

3. Computers: One of a set of symbols, such as letters or numbers, that are arranged to express information; the numerical code representing such a character.

Etymology (EN): M.E. carecter “distinctive mark,” from O.Fr. caractère, from L. character, from Gk. kharakter “graving tool, its mark,” from kharassein “to engrave,” from kharax “pointed stick.”

Etymology (PE): 1, 2) Serešt “nature, temperament, constitution; mixed,” sereštan “to mix, mingle; knead;” serišom “glue;” Mid.Pers. srištan “to mix, knead;” cf. Av. ham-sriš- “to put together;” Skt. śres- “to cling, stick, be attached;” Proto-Ir. root *sraiš- “to put together, attach” (Cheung 2007).
Sereštâr with -âr, contraction of âvar agent noun of âvardan “to bring; to cause, produce,” → format.