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

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

→ 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.

→ celestial; → equator.

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

→ 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.

→ celestial; → horizon.

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

→ celestial; → latitude.

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

→ celestial; → longitude.

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.

→ celestial; → mechanics.

Mekânik, → mechanics; âsmâni, → celestial.

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

→ celestial; → meridian.

→ astronomical object.

→ 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.

→ 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.

→ 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.

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").

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.

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.

→ 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.

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.

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).

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.

→ 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.

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."

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.

→ 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.

→ center; → gravity.

Gerânigâh, from gerâni→ gravity + -gâh "place."