An Etymological Dictionary of Astronomy and Astrophysics

A group of very rare → carbonaceous chondrites which are unusual because they do not have → chondrules. They are thought to be the most primitive of all meteorites. As a result of alteration, they lack chondrules and → CAIs, but contain up to 20% water, as well as various alteration minerals. Only five CI chondrite falls are known, and of these, only four are massive enough for multiple chemical analyses. The Orgueil meteorite is the most massive of CI chondrites.

See also: C for → carbon, I stands for Ivuna meteorite that fell in Tanzania in 1938; → chondrite.

A mineral, mercuric sulphide, HgS, which is the primary → ore for the production of → mercury. It is a → crystalline solid with a bright → red
color. Cinnabar is highly toxic.

See also: From O.Fr. cinabre, from L. cinnabaris, from Gk. kinnabari, maybe ultimately from Pers. šangarf “red lead, cinnabar,” of unknown origin.

Being, having, characterized by, or occurring in approximately 24-hour periods or cycles, as of biological activity or function (Merriam-Webster.com).

See also: From L. circa “about,” → circum-,

• diem, accusative singular of dies “day,” → diurnal.

Any of several physical, mental and behavioral changes that follow a roughly 24-hour cycle, responding primarily to light and darkness in an organism’s environment. Circadian rhythms are found in most living things, including animals, plants and many tiny microbes.

See also: → circadian; → rhythm.

The Compasses. A small, faint → constellation in the southern hemisphere near → Musca and → Triangulum Australe, at about 15h right ascension and 60° south declination. Abbreviation: Cir; genitive Circini.

Etymology (EN): L. circinus “pair of compasses,” from circus “circle, ring,” from or akin to Gk. kirkos “a circle,” from PIE kirk- from base (s)ker- “to turn, bend” (from which derives also Pers. carx “wheel, cycle,” → cycle).

Etymology (PE): Pargâr, → compasses.

A closed curve lying in a plane and so constructed that all its points are equally distant from a fixed point in the plane.

Etymology (EN): From O.Fr. cercle, from L. circulus “small ring,” dim. of circus “ring,” from or akin to Gk. kirkos “a circle,” from PIE kirk- from base (s)ker- “to turn, bend,” related to Pers. carx “wheel, everything revolving in an orbit, circular motion, chariot.”

Etymology (PE): Parhun “circle” in Mod.Pers. classical texts, from Proto-Iranian *pari-iâhana- “girdle, belt,” from pari-, variant pirâ-, → circum-, + iâhana- “to girdle,” cf. Av. yâh- “to girdle.” The Pers. word pirâhan “shirt” is a variant of parhun. Gk. cognate zone “girdle."
Dâyeré, from Ar.

A small circle on the celestial sphere parallel to the horizon. The locus of all points of a given altitude. Also called → almucantar, → altitude circle, → parallel of altitude.

See also: → circle; → altitude.

1. A circle of the celestial sphere, parallel to the ecliptic.
   
2. A circle on the terrestrial surface parallel to the equator, along which longitude is measured.

See also: → circle; → latitude.

1. A great circle of the celestial sphere, from the pole to the ecliptic at right angles to the plane of the ecliptic.
   
2. A great circle on the terrestrial surface that meets the North and South poles and connects all places of the same longitude.

See also: → circle; → longitude.

1. General: A closed, usually circular line that goes around an object or area.
   

2. Physics: → electric circuit.

Etymology (EN): From O.Fr. circuit, from L. circuitus “a going around,” from stem of circuire, circumire “go around,” from circum “around,” → circum- + -ire “to go” (cf. Gk. ienai “to go,” Skt. eti “goes,” O.Pers. aitiy “goes,” Av. aeiti “goes,” Mod.Pers. âyad “comes,” PIE *ei- “to go, to walk.”

Etymology (PE): Gardrâh, from gard “turning round, revolving,”
from gardidan “to turn, to change” (Mid.Pers. vartitan, Av. varət- “to turn, revolve,” Skt. vartati, L. vertere, O.H.G. werden “to become;” PIE *werto, *wer-)

• râh “way, path,” from Mid.Pers. râh, râs “way, street” (Mid.Pers. rah, ras “chariot”), from Proto-Iranian *rāθa-; cf. Av. raθa- “chariot;” Skt. rátha- “car, chariot,” rathyā- “road;” L. rota “wheel,” rotare “to revolve, roll;” Lith. ratas “wheel;” O.H.G. rad; Ger. Rad; Du. rad;
  O.Ir. roth; PIE *roto- “to run, to turn, to roll”).
  Barqrâh, from barq, → electricity, + râh, as above.

1. Having the form of a circle.
   

2. Moving in or forming a circle or a circuit.

Etymology (EN): M.E. circuler, O.Fr. circuler, from L. circularis, from circulus, → circle, + -aris “-ar,” variant of → -al, joined to words in which an l precedes the suffix (circular; lunar; singular).

Etymology (PE): Dâyere-yi, parhuni, from dâyeré or parhun→ circle + -i adj. suffix.

A → magnetic field whose lines of force (→ line of force) run around the perimeter of the magnet.

See also: → circular; → magnetic; → field.

Motion in which an object moves in a circle at a constant speed. The velocity, however, changes not because the magnitude of the velocity changes, but because its direction changes. The changing velocity creates an acceleration, called → centripetal acceleration. This acceleration results from the → centripetal force.

See also: → circular; → motion.

The path of a object in → circular motion.

See also: → circular; → orbit.

The → polarization of an → electromagnetic radiation in which the electric field vector describes a circle about the direction of propagation at any point in the path of the radiation. Circular polarization is a combination of two perpendicular → linearly polarized waves that are 90 degrees out of phase with each other. Circular polarization may be referred to as “right-hand” or “left-hand,” depending on the rotation direction as viewed by the observer.

See also: → circular; → polarization.

Circular band-pass interference filter whose thickness and central wavelength vary along the perimeter. They are used in low-resolution spectrophotometers mainly in the infra-red.

See also: → circular; → variable; → filter.

Light exhibiting → circular polarization.

See also: → circular; → polarized; → light.

The continuous movement of something from place to place or in an enclosed space. → meridional circulation.

Etymology (EN): M.E. circulacioun, from M.Fr. circulation or directly from L. circulationem, from circulare “to form a circle,” from circulus “small ring,” → circle.

Etymology (PE): Parhuneš, verbal noun from parhunidan, from parhun, → circle.

L. prefix meaning “around, round about.”

Etymology (EN): From L. circum “around,” accusative of circus “circle, ring,” from Gk. kirkos, krikos “ring,” PIE *sker-, *ker- “to turn, bend.”

Etymology (PE): Pirâ- “around, about,” variants par-, fer-, pâl- (as in ferdows, pardis, pâliz, from Av. pairidaeza- “enclosure, park”); Mid.Pers. pêrâ;
O.Pers. pariy “around, about;” Av. pairi “around, over;” cf. Skt. pari;
Indo-Iranian *pari- “around;” Gk. peri “around, about, beyond;” L. per “through;” PIE base *per- “through, across, beyond.” The word paradize, with various forms in European languages,
is a loan from Av. pairidaeza- “enclosure, park” (other Av. examples: pairifrâsa- “asking round about,” pairivâra- “circumvallation”).

Of or relating to an object that revolves around a → binary system.

See also: → circum- + → binary.

A relatively thin structure of matter composed mainly of gas and dust that orbits both the → primary and → secondary stars in → binary systems.

See also: → circumbinary; → disk.

An → accretion disk formed around a → black hole.

See also: → circum-; → black; → hole.

In a triangle, the point where the perpendicular bisectors of the triangle’s sides converge.

See also: → circum-; → center.

A circle which passes through all three vertices of a triangle Also “Circumscribed circle”.

See also: → circum-; → circle.

1. The boundary line of a circle.
   
2. The boundary line of a figure, area, or object.

Etymology (EN): From M.E., from O.Fr. circonference, from L. circumferentia, from circumferens, circumferent-, pr.p. of circumferre “to carry around,” from → circum- + ferre “to carry,” from PIE root *bher-; “to carry;” cf. Av./O.Pers. bar- “to bear, carry,” barəθre “to bear (infinitive),” barəθri- “a female that bears (children), a mother,” Mod.Pers. bordan “to carry,” Skt. bharati “he carries,” Gk. pherein, P.Gmc. *beranan (O.H.G. beran, Goth. bairan “to carry”).

Etymology (PE): Pirâmun, from Mid.Pers. pêrâmôn, from O.Pers./Av. mâ-, mây- “to measure,” from PIE *me- “measure,” cf. Skt. mati “measures,” matra “measure,” Gk. metra “lot, portion,” L. metri “to measure.” In Mod.Pers. this stem is extant in peymaân, peymaâné, âzmun, âzmâyeš.

An → affix made up of two separate parts which surround and attach to a base.

See also: → circum-; → affix.

The interface between a galaxy and the → intergalactic medium. The circumgalactic medium comprises gas located in the → halo of a galaxy extending out to the → virial radius.

See also: → circum-; → galactic.

Surrounding or revolving around the Moon.

See also: Circumlunar, from → circum- + → lunar.

Situated around a → nucleus, as of a → circumnuclear disk.

See also: → circum- + → nuclear.

A thick disk of gas and dust clouds surrounding the → Galactic Center up to about 20 → light-years. The disk is very clumpy; the → clumps have densities of several 10⁵ particles/cm³, radii of about 0.3 light-years, and gas temperatures above 100 K. The hydrogen mass of the disk is a few 10⁴ → solar masses. Such
circumnuclear disks are present also in other galaxies.

See also: → circumnuclear; → disk.

Situated around or near a pole, as of the Earth or the sky. → circumpolar star.

See also: → circum-; → polar.

Star that, from a given observer’s → latitude, does not rise or set, but circles around the → celestial pole. To be circumpolar, a star must have a polar distance that is less than the observer’s latitude. Whether a given star is circumpolar at the observer’s latitude (φ) may be calculated in terms of the star’s → declination (δ). The star is circumpolar if φ + δ ≥ +90° (observer in northern hemisphere), or φ + δ ≤ -90° (observer in southern hemisphere).

See also: → circumpolar; → star.

To draw a line around; encircle.

Etymology (EN): L. circumscribere “to draw a line around, confine,” from → circum- + scribere “write,” from PIE *skreibh-, from *sker- “to cut, incise.”

Etymology (PE): Pirâkašidan, from pirâ-, → circum- + vešidan “to write,” → inscribe.

A sphere containing a polyhedron (such as a pyramid) all of whose vertices lie on the surface of the sphere. The polyhedron so contained is said to be inscribed in the sphere.

See also: Circumscribed p.p. of → circumscribe; → sphere.

Surrounding or revolving around the Sun, such as circumsolar space, circumsolar dust.

See also: Circumsolar, from → circum- + → solar.

Watchful and discreet; cautious; prudent:

See also: → circum-; → suspect.

Circumspect observation or action; caution; prudence.

See also: → circumspect.

A condition or fact attending an event and having some bearing on it.

Etymology (EN): L. circumstantia “surrounding condition,” neut. pl. of circumstans, pr.p. of circumstare “to stand around,” from → circum- + stare “to stand” from PIE *sta- “to stand.”

Etymology (PE): Pirâstâd, from pirâ-,
→ circum-, + âstâd, istâd “standing,” from istâdan “to stand,” Mid.Pers. êstâtan, O.Pers./Av. sta- “to stand, stand still; set,” Av. hištaiti, cf. Skt. sthâ- “to stand,” âsthâ-
“condition, circumstance,” Gk. histemi “put, place, weigh,” stasis “a standing still,” L. stare “to stand.”

Surrounding or occurring around a star.

See also: Circumstellar, from → circum- + → stellar.

Any concentration of material in the form of a disk orbiting around a star. → accretion disk; → protoplanetary disk.

See also: → circumstellar; → disk.

Interstellar → dust grains localized around various types of stars, such as → asymptotic giant branch stars. Circumstellar dust occurs in the form of a spherical shell or a disk and is at the origin of an → infrared excess for the central star. See also → circumstellar matter.

See also: → circumstellar; → dust.

A very extensive envelope of cold gaseous materials surrounding evolved cool
stars, notably → red giants, → red supergiants (→ Mira variables), or → asymptotic giant branch stars. The typical size of such envelopes is several thousands times that of the stellar radius and their temperature ranges from 1000 to10 K. Circumstellar envelopes result from mass loss from the central star (10^-7 to 10^-4→ solar masses per year) and expand with moderate velocities (10 to 15 km sec^-1). The low temperature of the envelope is at the origin of the formation of molecules, which in certain conditions provide → maser emission (H₂O, OH, SiO). Similarly, dust grains form in the envelope produce an → infrared excess emission.

See also: → circumstellar; → envelope.

The circumstances or physical conditions related to the immediate surroundings of a star.

See also: → circumstellar; → environment.

A zone around a star within which a planet can have temperatures that permit liquid water, depending on the luminosity of the star and the distance of the planet from it.

See also: → circumstellar; → habitable zone.

Maser emission from molecules in the circumstellar envelopes of → red giants, and also from regions around → protostars.

See also: → circumstellar; → maser.

Dust, gas and plasma around stars, generally present in the form of stellar winds or nebulae ejected by the stars.

See also: → circumstellar; → matter.

A stream of matter into the interstellar medium from a central star.

See also: → circumstellar; → outflow.

A shell of dust, molecules, and neutral gas around an evolved
star resulting from an intensive mass loss phase, such as the asymptotic giant branch phase for low- and intermediate mass stars and LBVs or supernovae for massive stars.

See also: → circumstellar; → shell.

A colorful halo centered on the zenith, appearing when the solar elevation above the horizon is not too high (< 32°).

See also: → circum-; → zenithal; → arc.

Lying between the Earth and the orbit of the Lune. → translunar.

Etymology (EN): L. cis, cistra “on this side,” cf. Gk. ekeinos “that person,” E. he, it, O.H.G. he.

Etymology (PE): Insuumâhi, insumângi, from insu “this side,” from in “this”

• su “side” + mâhi, mângi→ lunar, → moon.

Any large town or populous place.

Etymology (EN): M.E. cite, from O.Fr. cite “town, city,” from L. civitas “citizenry; community,” from civis “native, townsman;” related to L. cuna “cradle; bed;” Gk. kome “village;” Skt. śiva- “auspicious, dear;” O.E. ham “dwelling, house, village;” E. home; Ger. Heim (→ hamlet); Iranian dialects kiye “house, home;” Xonsâri ki “house;” Anâraki xiya, Tâti Karingân kâ, Sangesari keh “house, home;” PIE *kei- “to lie; bed.”

Etymology (PE): Šahr “city,” from
Mid.Pers. šahr “land, country, city;” O.Pers. xša- “to rule,” pati-xša- “to have lordship over,” Xšyāršan- “hero among kings” or “ruling over heroes” the proper name of the Achaemenid emperor Helenized as Xerxes, upari.xšay- “to rule over,” xšāyaθiya- “king;” Mid.Pers. šâh “king,” pâdixšâ(y) “ruler; powerful; authoritative;”
Mod.Pers. šâh “king,” pâdšâh “protecting lord, emperor, monarch, king,” šâyestan “to be worth, suit, fit;” Av. xšā(y)- “to rule, have power,” xšayati “has power, rules,” xšāyô “power;” cf. Skt. ksā- “to rule, have power,” ksáyati “possesses;” Gk. ktaomai “I acquire,” ktema “piece of property;” PIE base *tkeh- “to own, obtain.”

Of or relating to citizens and their interrelations with one another or with the state.

Etymology (EN): M.E., from L. civilis “of or proper to a citizen,”
from civis “citizen, townsman,” from PIE *kei- “to lie, homestead;” → city.

Etymology (PE): Šârin, from šâr “city,” variant šahr; Mid.Pers. šahr “city, country, land”
(O.Pers./Av. xšaθra- “kingship, kingdom,” (Skt. ksatra-), from xšay-, “to rule;” cf. Skt. ksayati “possesses;” Gk. ktaomai “I acquire,” ktema “piece of property”) + -in suffix of adjectives, relations and agent nouns (as in qamin “sorrowful,” nušin “sweet, agreeable (thing).”

→ Mean solar time.

See also: → civil; → time.

The time between sunset or sunrise and the moment when the Sun’s center lies 6° below the horizon. It is followed or preceded by → nautical twilight. See also → astronomical twilight. In the morning, this twilight phase ends at sunrise. In the evening it begins at sunset. Civil twilight is the brightest of the three twilight phases. As the Earth’s atmosphere scatters and reflects much of the Sun’s rays, artificial lighting is generally not required in clear weather conditions to carry out most outdoor activities. Only the brightest stars and planets, like Venus and Jupiter, can be seen with the naked eye.

See also: → civil; → twilight.

1. An advanced state of human society, in which a high level of culture, knowledge, production, and legal organization has been reached.
   The people or nations that have reached such a state.
   

2. The act or process of civilizing or being civilized.

See also: verbal noun of → civilize.

1. To cause to evolve out of a primitive state as to technical, moral, or intellectual matters.
   

2. To acquire the customs and manners of a civil community.

See also: → civil + → -ize.

1. Of a society or country, having well-organized laws and rules about
   way of life.
   

2. Cultured, polite.

See also: Past participle of → civilize.