An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A suffix of nouns, often corresponding to verbs ending in -ize or nouns ending in → -ism, that is used to form an agent noun indicating adherence to a certain doctrine or custom, practicing a particular skill or profession, and so on.

From Fr. -iste, from L. -ista, from Gk. -istes.

-bâvar, from bâvar "belief;" Mid.Pers. wâbar "belief;" Proto-Iranian *uar- "to choose; to convince; to believe;" cf. Av. var- "to choose; to convince" varəna-, varana- "conviction, faith;" O.Pers. v(a)r- "to choose; to convince;" Skt. vr- "to choose," vara- "choosing."
-gerâ, from gerâyidan "to incline toward; to intend; to make for," infinitive of gerâ, the etymology of which is not clear. Gerâ may be a variant of Mod.Pers. kil "bent, inclined" (k/g and l/r interchanges), from PIE base *klei- "to lean, incline," cognate with L. clinare "to bend" (E. declination, inclination, etc.), Gk. klinein "to cause to slope, slant, incline," Skt. sri- "to lean," O.Pers. θray-, Av. sray- "to lean," (cf. Ger. lehnen, E. lean).
-gerow, -gerav present stem of geravidan "to believe, confide in; to obey;" Mid.Pers. virrôy(i)stan , related to bâvar, as above, ultimately from Proto-Iranian *uar- (Cheung 2007).
-gar 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").
-mand possession suffix, from Mid.Pers. -omand; O.Pers./Av. -mant; cf. Skt. -mant.

A suffix of adjectives denoting "relating to, characteristic of;" often in adjectives corresponding to nouns in → -ism or nouns in → -ist.

L. -isticus, from Gk. -istikos, → -ist + → -ic.

The instantaneous action of a body on another body independently of the distance separating them. The description of → gravity by → Newton's law and → electrostatics by → Coulomb's law are examples of action at a distance. According to Newton, → gravitation acts directly and instantaneously between two objects. For example, if the Sun should suddenly break apart, the Earth's orbit would be affected instantaneously. However, action at a distance violates the → principle of relativistic causality. According to → general relativity, gravitational effects travel at the → speed of light. For modern physics there is no instantaneous action at a distance.

→ action; → distance.

An especially active, vigorous advocate of a cause, especially a political cause (Dictionary.com).

Agent noun from → activism.

1) The ratio of an object's → linear size (l) to its → angular size (δθ, in → radians), that is D_A = l/δθ. It is used to convert observed angular separations into proper separations at the source.

2) In cosmology, a distance defined as the ratio of an object's physical transverse size (l) to its angular size (δθ). It is used to convert angular separations in telescope images into proper separations at the source. The angular diameter distance is defined by: D_A = l / δθ. Consider a light source of size l at r = r₁ and t = t₁ subtending an angle δθ at the origin (r = 0, t = t₀). The proper distance between the two ends of the object is related to δθ by: δθ = l / [a(t₁). r₁], where a(t₁) is the → scale factor at the present epoch. Therefore, D_A = r₁ / (1 + z). The angular diameter distance has the particularity that it does not increase infinitely with z→ ∞. It gets its maximum value at a → redshift of ~ 1 and then decreases for higher z. Therefore, more distant objects appear larger in angular size. This is explained by considering the size of the Universe when the light of the object was emitted. At that time the Universe was smaller and therefore the object occupied a larger fraction of the size of the Universe. In other words, objects appear larger because the entire Universe acts as a → gravitational lense.

→ angular; → diameter; → distance.

Between two points A and B, the angle → subtended by lines drawn from an observing point O to A and B. Same as → angular separation.

→ angular; → distance.

Same as → angular diameter distance.

→ angular; → size; → distance.

The time interval of 27.554 551 days (27d 13h 18m 33.2s), on average, between two successive passages of the Moon through the → perigee of its orbit.

Anomalistic from → anomaly.

Pirâzamini from pirâzamin, → perigee.

Anomalistic from → anomaly.

Pirâhuri from pirâhur, → perihelion.

The distance between the → Sun and an → object in orbit around it when they are at their farthest approach.

→ perihelion; → distance.

The angular distance between two celestial bodies (e.g. the components of a binary star system), expressed in degrees, minutes and seconds of arc.

→ apparent; → distance.

Put in modern notation, if α and β are acute angles and if β <α, then sin α / sin β <α / β < tan α / tan β. Aristarchus probably used this inequality to show that the Sun is between 18 and 20 times as far from the Earth as the Moon is.

Aristarchus of Samos (c.310-c.230 BC); → inequality.

Any of the four main → proposition forms treated in Aristotle's → syllogism:
The A form (universal affirmative): All P's are Q's,
The E form (universal negative): No P's are Q's,
The I form (particular affirmative): Some P's are Q's, and
The O form (particular negative) Some P's are not Q's.

Greek philosopher Aristotle (384-322 BC); → form.

1) An agreement between opposing armies to stop fighting for a particular time, especially in order to discuss possible peace; truce
2) A formal agreement, especially between nations, to end combat.

From Fr. armistice, from L. arma "arms" + -stitium, from sistere "to cause to stand," → solstice.

Nâjangân, literally "state of no war," from nâ- "no, not," → un-, + jang, → war, + -ân suffix of time and place.

The study of the chemical interactions between the gas and dust of the interstellar medium.

Astrochemistry, from → astro- "star" + → chemistry.

Axtaršimi, from axtar, → astro-, + šimi, → chemistry.

A scientist who studies → astrophysics.

→ astro-; → physicist. The term astrophysicist was introduced by Greenwich astronomer Edwin Dunkin in 1869.

Of or relating to → ballistics.

A missile that after being launched and guided in the early part of its flight, travels unpowered in a ballistic trajectory.

→ ballistic; → missile.

Transfer of microbes and biochemical compounds from a planet to another due to meteoric impacts. Debris being knocked off a planet like Mars can reach escape velocity and enter the atmosphere of another planet with passenger micro-organisms intact.

→ ballistic; → panspermia.

A curved path followed by an unpowered object that is being acted upon only by gravitational forces and the friction of the medium through which it moves.

→ ballistic; → trajectory.