An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 1307
crescent Moon visibility
  دیاری ِ هلال ِ ماه   
diyâri-ye helâl-e mâh

Fr.: visibilité du croissant lunaire   

The first sighting of the → New Moon after its → conjunction with the Sun. Although the date and time of each New Moon can be computed exactly, the visibility of the lunar → crescent as a function of the → Moon's age depends upon many factors and cannot be predicted with certainty. The sighting within one day of New Moon is usually difficult. The crescent at this time is quite thin, has a low surface brightness, and can easily be lost in the → twilight. Generally, the lunar crescent will become visible to suitably-located, experienced observers with good sky conditions about one day after New Moon. However, the time that the crescent actually becomes visible varies from one month to another. The visibility depends on sky conditions and the location, experience, and preparation of the observer. Ignoring atmospheric conditions, the size and brightness of the lunar crescent depend on the → elongation which in turn depends on several factors: 1) The Moon's elongation at New Moon (the elongation of the Moon at New Moon is not necessarily 0). 2) The speed of the Moon in its elliptical orbit. 3) The distance of the Moon, and 4) The observer's location (parallax). The combined effect of the first three factors gives geocentric elongation of the Moon from the Sun at an age of one day which can vary between about 10 and 15 degrees. This large range of possible elongations in the one-day-old Moon is critical (US Naval Observatory).

crescent; → moon; → visibility.

crescent width
  پهنای ِ هلال، ~ برن   
pahnâ-ye helâl, ~ barn

Fr.: largeur de croissant   

The width of the lit area of the → Moon measured along the Moon's diameter.

crescent; → width.

setiq (#)

Fr.: crête   

The highest point or upper part of a wave.

From O.Fr. creste "tuft, comb," from L. crista "tuft, plume; rooster's comb."

Setiq "summit; anything standing upright," from O.Pers./Av. sta- "to stand, stand still; set," Mod.Pers. istâdan "to stand" (cf. Skt. sthâ- "to stand," Gk. histemi "put, place, weigh," stasis "a standing still," L. stare "to stand") + adj. suffix -iq, variants -ig, -ik, → -ics.


Fr.: Crétacé   

A period of → geologic time which began at the end of the → Jurassic period approximately 145 million years ago and extended to approximately 65 million years ago.

From L. cretaceus, from cret(a) "chalk, clay," + → -aceous, because the geological remains of this period contain heightened chalk deposits.

Gacâsâ, from gac "chalk," Mid.Pers. gac + -âsâ, → -aceous.

Cretaceous-Paleogene extinction event
  رویداد ِ خاموشی ِ گچاسا-پارینزاد   
ruydâd-e xâmuši-ye Gacâsâ-Pârinzâd

Fr.: extinction Crétacé-Tertiaire   

The → mass extinction event that destroyed the dinosaurs and a majority of other species on Earth approximately 65 million years ago. This event is believed to have been the impact of a 10 km-size → asteroid or → comet nucleus and its aftereffects, including a severe → impact winter. The collision would have released the energy equivalent to 100 million megatonnes (teratonnes) of → TNT, i.e. more than 109 times the energy of the atomic bomb dropped on Hiroshima on August 6, 1945. Same as the → Cretaceous-Tertiary event.

Cretaceous; → Paleogene; → extinction; → event.

Cretaceous-Tertiary event
  رویداد ِ K-T   
ruydâd-e K-T (#)

Fr.: événement K-T   

See → Cretaceous-Paleogene extinction event.

K, representing the "→ Cretaceous period," and T the "→ Tertiary;" → event.


Fr.: équipage, équipe   

A group of persons acting or working together.

M.E. crewe "augmentation, reinforcement, body of soldiers," from M.Fr. crue, from O.Fr. creue "an increase, recruit, military reinforcement," from p.p. of creistre "grow," from L. crescere "grow, arise," → crescent.

Koran, variants korand, korang "a troop, a circle of people" (Dehxodâ).

bazah (#)

Fr.: crime   

An action or an instance of negligence that is deemed injurious to the public welfare or morals or to the interests of the state and that is legally prohibited (

M.E., from O.Fr. crimne, from L. crimen "charge, indictment, accusation; offense."

Bazah, from Mid.Pers. bazag "crime, misdeed," bazagkâr "evil-doer," Parthian bzg "evil, wicked."

  ۱) بزهی؛ ۲) بزه‌کار   
1) bazahi; 2) bazahkâr

Fr.: criminel   

1) Of the nature of or involving crime.
2) A person guilty or convicted of a crime.

L. criminalis, → crime; → -al.


Fr.: crise   

A decisive stage or turning point in the course of something, especially in a sequence of events or an acute disease.

M.E., from Latinized from of Gk. krisis "turning point in a disease," literally "judgment, selection," from krinein "to separate, decide, judge;cf. " L. cribrum "sieve," crimen "judgment, crime;" → critique.

Paržané, from paržan, present stem of paržanidan "to separate, sift, → critique," + a suffix of relation.


Fr.: net   

1) Notably sharp, clear-cut, and clear.
2) Noticeably neat (

M.E, from O.E., from L. crispus "curled," cognate with Walsh crych "curly."

Tuj (Kurmanji Kurd.) variant of tiz, → sharp.

crisp set
  هنگرد ِ توج   
hangard-e tuj

Fr.: ensemble net   

A classical set that allows only full membership or no membership at all for its elements, as contrasted with a → fuzzy set. Crisp set can be viewed as a restricted case of the more general fuzzy set concept.

sanjidâr (#)

Fr.: critère   

A standard or rule that can serve as basis for a judgment or decision.

From Gk. kriterion "means for judging, standard," from krites "judge," from krinein "to separate, distinguish, judge." L. cribrum "sieve" *krei- "to sieve, discriminate, distinguish."

Sanjidâr verbal noun from sanjid- past tense stem of sanjidan "to compare; to measure" (Mid.Pers. sanjidan "to weigh," from present tense stem sanj-, Av. θanj- "to draw, pull;" Proto-Iranian *θanj-) + suffix -âr.

  پرژنکار، پرژنگر   
paržankâr, paržangar

Fr.: critique   

A person who judges, evaluates, or criticizes.

M.E., from M.Fr. critique, from L. criticus "a judge, literary critic," → critique.

Paržangar, from paržan present stem of paržanidan, "criticize", → critique, + -kâr, -gar suffixes of agent nouns, → -or.


Fr.: critique   

1) Of or pertaining to → critics or → criticism.
2) Of, relating to, or being a state or level at which a significant change takes place (

critic; → -al.

critical angle
  زاویه‌ی ِ پرژنی   
zâviyeh-ye paržani

Fr.: angle critique   

Angle of incidence of light proceeding from a denser medium toward a thinner, at which grazing refraction occurs (angle of refraction 90°).

critical; → angle.

critical Bonnor-Ebert mass
  جرم ِ پرژنی ِ بونور-ابرت   
jerm-e paržani-ye Bonnor-Ebert

Fr.: masse critique de Bonnor-Ebert   

The upper value of mass that a → Bonnor-Ebert sphere must have in order that → hydrodynamic equilibrium be maintained. This → critical mass is given by: Mcrit = 1.18 (a4/G3/2)Pext-1/2, where a = (kT/m)1/2 is the isothermal → sound speed inside the sphere, G is the → gravitational constant, and Pext the pressure of the external medium (see, e.g., F. H. Shu, 1977, ApJ 214, 488).

critical; → Bonnor-Ebert mass.

critical density
  چگالی ِ پرژنی   
cagâli-ye paržani

Fr.: densité critique   

1) Cosmology: The average density of matter in the Universe that would be needed to eventually halt the → cosmic expansion. In a spatially → flat Universe, the critical density is expressed by ρc = (3c2/8πG)Ht2, where c is the → speed of light, G is the → gravitational constant, and Ht the → Hubble parameter. The critical density is currently 9.3 × 10-30g cm-3, about 6 hydrogen atoms per cubic meter (for H0 = 70 km s-1 Mpc-1).
2) In → gravitational lensing, the minimum density that would be needed by an intervening object to bend light rays. It is expressed by: Σ = (c2/4πG)(dos/doldls), where c is the speed of light, G is the gravitational constant, dos, dol, and dls represent angular diameter distances between the observer and the source, the observer and the lens, and the lens and the source respectively. It has units of mass per unit solid angle.
3) Radiative processes: The density at which the collisional → de-excitation rate equals the → radiative transition rate. The critical density for level j is given by: nc = Σi < j Aji = Σi ≠ j qji, where Aji is the → Einstein coefficient of → spontaneous emission and qji is the rate for collisional de-excitation of → energy level j, summed over all possible processes. This expression often simplifies to the ratio of two numbers, since in many cases there is a single important path for emission and a dominant collisional de-excitation process. In the low density limit the → emissivity is proportional to the product Ne (electron density) x Ni (ion density), whereas for densities exceeding the critical density, the emissivity is proportional to Ni. Thus, line emission in a nebula occurs most efficiently near the critical density.

critical; → density.

critical mass
  جرم ِ پرژنی   
jerm-e paržani

Fr.: masse critique   

Of a fissile material (235U or 239Pu), the minimum mass needed for a sustained nuclear chain reaction, as in an atomic bomb.

critical; → mass.

critical metallicity
  فلزیگی ِ پرژنی   
felezigi-ye paržani

Fr.: métallicité critique   

The → metallicity of a → star-forming  → molecular cloud when → cooling → rates by → metals dominate the → gravitational  → heating during → protostellar collapse. The minimum → Jeans mass achieved by gravitational → fragmentation depends on the presence/absence of → coolants in the cloud. Since cooling rate in metal lines is more efficient than in primordial molecular lines (H2 and HD), metals favor fragmentation in gas and formation of → low-mass stars.

critical; → metallicity.

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