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

Relating to an → apsis.

→ apsis; → -al.

→ Rotation of the → line of apsides in the plane of the orbit in the same direction as the → revolution of the → secondary body. The major axis of the Earth's orbit rotates by 11.6 arcseconds per year.

→ apsidal; → motion.

→ advance of perihelion, → relativistic precession.

→ apsidal; → precession.

The line connecting the two apsides, i.e. the major axis of an elliptical orbit. → apsis.

Apsides, pl. of → apside; → line.

The point of greatest or least distance of the orbit of a celestial body from a center of attraction. The closest point is the → periapsis, the further point the → apoapsis.

L. apsis "arch, vault," from Gk. hapsis "loop, arch," from haptein "fasten together".

Mod.Pers. habâk "top of the head; the summit of a mountain".

Exactly suitable; appropriate; suited to a purpose.

M.E., from L. aptus "fitted, suitable, fastened," from p.p. of *apere "to fasten;" akin to Hittite hap- "to attach;" PIE *ap- "to grasp, take, reach".

Niyâw "apt, suitable, appropriate," from Mid.Pers.

The Bird of Paradise. A constellation in the southern hemisphere, at R.A. = 16 h, Dec. = -75°. Abbreviation: Aps; genitive form: Apodis.

L. apus "a kind of swallow," from Gk. apous "without feet, sand martin," from → a- "without" + pous "foot".

Morq-e behešti "bird of paradise," from morq "bird" + behešt "paradise".

Several → meteor showers that have their → radiants in the constellation → Aquarius. The main showers are:
1) Eta Aquarids, which occurs early in May and is apparently associated with → Halley's comet, and
2) Delta Aquarids occurring in early August.

Aquarids, from → Aquarius constellation + → -ids suffix denoting "descendant of, belonging to the family of."

Âbkašiyân, from Âbkaš + -iyân, → -ids.

The Water Bearer. An extended southern constellation composed of rather faint stars (R.A. about 23h, Dec. about -15 deg). One of the signs of the → Zodiac, it is surrounded by → Pegasus, → Equuleus, and → Delphinus to the north, → Aquila to the west, → Pisces Austrinus and → Sculptor to the south, and → Cetus to the east. Abbreviation: Aqr, genitive from: Aquarii.

Aquarius, L. "water carrier," literally "of the water," translation of Gk. Hydrokhoos "the water-pourer," old Gk. name of this constellation.

Âbkeš "water carrier or drawer," from âb "water" (Mid.Pers. âb "water;" O. Pers. ap- "water;" Av. ap- "water;" cf. Skt. áp- "water;" Hitt. happa- "water;" PIE āp-, ab- "water, river;" cf. Gk. Apidanos, proper noun, a river in Thessalia; L. amnis "stream, river" (from *abnis); O.Ir. ab "river;" O.Prus. ape "stream;" Lith. upé "stream;" Latv. upe "brook") + keš "drawer," contraction of kešandé, from kešidan/kašidan "to carry, draw, extract, trail, drag" (Mid.Pers. kešidan "to draw, pull;" Av. karš- "to draw; to plough," karša- "furrow;" cf. Skt. kars-, kársati "to pull, drag, plough," Gk. pelo, pelomai "to be busy, to bustle;" PIE base k^wels- "to plow").

The Eagle. A constellation on the celestial equator representing an eagle (R.A. about 19h30, Dec. about +5 deg). It is marked by the bright star → Altair (α Aquilae). Abbreviation: Aql, genitive form: Aquilae.

L. aquila "black eagle," fem. of aquilus "dark colored" (bird).

Šâhin "eagle," Av. saêna- "eagle," Skt. śyená- "eagle, falcon, hawk".

A long, dark structure located close to the → Galactic plane and occupying an area between longitudes l ~15° and ~35° and latitudes b ± 10° in the constellations Aquila, Serpens, and eastern Ophiuchus. The Aquila Rift is a complex of dust and → molecular clouds making part of → Gould's Belt in the → Orion Arm. The mass of the molecular gas, derived from → carbon monoxide (CO) observations (Dame et al. 2001, ApJ 547, 792), is in the range ~ 1-3 x 10⁵ → solar masses. A distance of ~260 pc has been estimated for the Aquila Rift, but it is uncertain. Recent Herschel observations have revealed a filamentary structure in the Aquila Rift and the presence of a population of → pre-stellar cores as well as → young stellar objects (André et al. 2010, A&A 518, L102; Bontemps et al. 2010, A&A 518, L85; Könyves et al. 2010, A&A 518, L106).

→ Aquila; → rift.

L. ara "fire altar," from PIE as- "to burn".

Âtašdân "a hearth, a fire-place; a movable coal grate," from âtaš "fire" (from Mid.Pers. âtaxš, âzar-, O.Pers. *âtar-, Av. âtar-, from Indo-Iranian *âtar-, compare with L. âter (feminine âtra) "black" (from "blackened by fire"); PIE *âter) + -dân suffix denoting recipient.

The astronomical activities that took place from the 8th to the 14th century in the Middle East, Central Asia, North Africa, and Moorish Spain. Arab/Arabic is not meant as an ethnic but rather a linguistic term. In fact a large number of Non-Arab scholars, mainly Persians, Mongols, and Spanish people, wrote their works in Arabic. Even so, many astronomical works were also produced in the other languages of this civilization, especially Persian and in the later centuries Turkish. For example, the main → zijs were originally written in Persian, a notable example being the Zij of Ulugh Beg (c. A.D. 1394-1449), a landmark in precise observations before the Renaissance. Therefore, the term Arabic astronomy is misleading. It also creates a disparity with respect to Western scholars who wrote in Latin. The term "Latin astronomy" is meaningless and as far as these scholars are concerned, the Latin adjective is not specified. For example, the expressions like "the Latin astronomer Copernicus," "the Latin physicist Newton," or "the Latin philosopher Leibniz" are not used. See also → Islamic astronomy.

M.E. arabik, from O.Fr. arabique, from L. Arabicus; → astronomy.

A → neutral point located at about 20° above the → antisolar point.

Named for François Arago (1786-1853), French physicist; → point

1) Based on individual will or choice rather than by reason or necessity.
2) Math.: Undetermined; of unspecified value. → arbitrary constant.

M.E., from O.Fr. arbitraire or directly from L. arbitrarius "depending on the will, uncertain," from → ad- "to" + baetere "to come, go."

Kâmsar, literally "at one's will," from kâm "desire, wish; cause, reason," → despite, + sar "person, individual," originally "→ head."

A constant quantity in → equations which takes various values but which remains unaffected by the changes in the values of the → variables of the equation. Most → differential equations have more than one → solution. In general, the number of arbitrary constants of an ordinary differential equation is given by the → order of the highest → derivative.

→ arbitrary; → constant.

1) In → graph theory, a → rooted tree that has a natural orientation in which all → paths are directed away from the → root. More specifically, a → directed graph in which, for a → vertex u, called the → root, and any other vertex v, there is exactly one → directed path from u to v.
2) Biology: The state of being branched, or treelike, in structure, appearance, growth, or other properties.

From Fr. arborescence, from → arborescent + → -ance.

Šâkedâri, nous from šâkedâr, → arborescent.

Having the shape or characteristics of a tree in growth, structure, or appearance.

From Fr. arborescent, from L. arborescent-, p.p. of arborescere "to grow into a tree," from arbor, arboris "tree."

Šâkedâr "having branches," from šâké, from šâxé, → branch, + dâr "having, possessor," from dâštan "to have, to possess," → charged.

1) General: Something shaped like a → curve or → arch.
2) Math.: A → segment of a → circle.
3) Electricity: A continuous luminous → discharge across a gap between two → electrodes, as in an arc lamp. → electric arc.
4) Astro.: The apparent path of a celestial body above and below the horizon.

M.E. ark, from M.Fr. arc "bow," from L. arcus "bow, arch" (cf. Goth. arhwazna "arrow," O.E. earh), PIE *arqu- "bowed, curved."

Kamân "arc, bow" from Mid.Pers. kamân, related to xam "curve," cf. Breton kamm "curved, bent," Gk. kampe "a corner, a joint," L. campus "a field," Lith. kampus "corner," PIE *kamb- "to bend, crook."

A unit of angular size equal to 1/60 of a degree.

→ arc; → minute.