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

The only naturally occurring → fissile isotope. Natural uranium has 0.7 percent of ²³⁵U; light water reactors use about 3 percent and weapons materials normally consist of 90 percent of this isotope.

→ uranium.

A → fertile isotope from which → plutonium-239 can be bred. It comprises 99.3 percent of natural uranium.

→ uranium.

The seventh planet from the Sun and the third largest, discovered by William Herschel in 1781. It has a diameter about 51,100 km, four times that of the Earth, and a mass 14.5 times Earth's mass. Uranus orbits the Sun at a distance over 19 times the Earth-Sun distance. Although it takes about 84 years for Uranus to make a revolution, it completes a fast rotation in only 17 and a half hours. Unlike the other planets, its axis of rotation lies mostly in the plane of the Solar System. Uranus is internally less active than the other giant planets, which added to its larger distance from the Sun, makes it colder. It has a dense atmosphere made of mostly molecular hydrogen (83 percent) and helium (15 percent), with two percent methane and traces of acetylene and other hydrocarbons. The planet's greenish-blue color is due to light scattering as in Earth's sky and the absorption of red light by its small amount of atmospheric methane. Uranus has a ring system and 27 known satellites.

L. Uranus, from Gk. Ouranos "heaven." In Gk. mythology he was the the primeval sky god, and responsible for both the sunshine and the rain. He was the son and husband of Gaia, the goddess of the Earth and the father of Titans.

A cycle of nuclear reactions, primarily among the iron group of elements, accompanied by a high rate of neutrino formation. Neutrinos carry away energy quickly leading to the cooling of the stellar core and a dramatic drop in the pressure. Due to this process in pre-supernova stars, the core becomes unable to support the weight of the overlying layers. These layers collapse onto the core and subsequently rebound and escape in the supernova explosion.

Named for the de Urca Casino in Rio de Janeiro, by George Gamow and Mario Schönberg, who first studied this process. Gamow is reported to have pointed to the similarity between the disappearance of money in the crowded gambling rooms of the Casino and the disappearance of electron energy into invisible neutrinos; → process.

1a) To push or force along; impel with force or vigor.
1b) To drive with incitement to speed or effort.
1c) To impel, constrain, or move to some action.
2) An act of urging; impelling action, influence, or force; impulse (Dictionary.com).

From L. urgere "to press hard, push forward, drive, compel,," from PIE root *ureg- "to push, shove, drive;" cf. Lith. verziu "tie, fasten, squeeze," vargas "need, distress;" O.C.S. vragu "enemy;" Gothic wrikan "to persecute;" O.E. wrecan "avenge; drive, hunt, pursue;" E. wreak "to inflict, to cause;" Av. uruuaj- "to walk," see below.

Garžidan, from Proto-Ir. *uraj- "to go forth" (Cheung 2007; on the model of *urad- "to soften," Baluchi grast "to cook in oil or water"); cf. Av. uruuaj- "to go forth, walk;" cf. Kurd. guš, gušin (?) "to press, squeeze, shake;" Skt. vraj- "to stride, walk, proceed;" cognate with L. urgere, as above (Cheung 2007).

The quality or state of being urgent; imperativeness; insistence.

Noun from → urgent.

Compelling or requiring immediate action or attention; imperative; pressing (Dictionary.com).

Adj. from → urge.

The Great Bear. An extensive and prominent constellation in the region of the north celestial pole, at approximately 10h 40m right ascension, +56° declination. The seven brightest stars of Ursa Major are known as the → Big Dipper. The region contains the planetary → Owl Nebula and the spiral galaxies M81 and M82. Abbreviation: UMa, Genitive: Ursae Majoris.

Ursa,from L. ursus "bear," cognate with Pers. xers, as below; Major irregular comparative adj. of magnus "large, great," cognate with Pers. meh "great, large" (Mid.Pers. meh, mas; Av. maz-, masan-, mazant- "great, important," mazan- "greatness, majesty," mazišta- "greatest;" cf. Skt. mah-, mahant-; Gk. megas; PIE *meg- "great").

In Gk. mythology, Zeus falls in love with the nymph Callisto, and they have a son named Arcus. To hide Callisto from the wrath of his wife, Hera, Zeus changed her into a bear. Later on, when Arcus saw the bear Callisto, drew his bow and prepared to shoot her. To prevent Arcus from killing his mother, Zeus placed them together in the sky as the Big Bear and the Little Bear.

Xers "bear," dialectal Tabari aš; Mid.Pers. xirs, Av. arša- "bear;" cf. Skt. rksa- "bear;" Gk. arktos; L. ursus; PIE base *rtko- "bear;" bozorg "large, magnificient, great;" Mid.Pers. vazurg "great, big, high, lofty;" O.Pers. vazarka- "great;" Av. vazra- "club, mace" (Mod.Pers. gorz "mace"); cf. Skt. vájra- "(Indra's) thunderbolt," vaja- "strength, speed;" L. vigere "be lively, thrive," velox "fast, lively," vegere "to enliven," vigil "watchful, awake;" P.Gmc. *waken (Du. waken; O.H.G. wahhen; Ger. wachen "to be awake;" E. wake); PIE base *weg- "to be strong, be lively."

A moving star cluster containing over 100 stars that are scattered over an area of sky more than 1,000 minutes of arc in diameter. The five brightest stars of the → Big Dipper as well as → Sirius belong to this → dynamical stream.

→ Ursa Major; → star; → cluster.

The Lesser Bear. A constellation situated in the northern hemisphere, at about 15h right ascension, +79° declination. Its two brightest stars, both of 2nd magnitude, are → Polaris, the present pole star, and → Kochab. Abbreviation: UMi, Genitive: Ursae Minoris.

Ursa,from L. ursus "bear," cognate with Pers. xers, as below; Minor "smaller, less," from minus related to L. minuere "make small;" cf. Gk. meion "less," minuthein "to lessen;" Skt. miyate "diminishes, declines;" O.E. minsian "to diminish;" PIE base *mei- "small."

Xers "bear," dialectal Tabari aš; Mid.Pers. xirs, Av. arša- "bear;" cf. Skt. rksa- "bear;" Gk. arktos; L. ursus; PIE base *rtko- "bear;" kucak "small;" Mid.Pers. kucak "small," related to kutâh "short, small, little," kudak "child, infant," kutulé, → dwarf; Mid.Pers. kôtâh "low," kôtak "small, young; baby;" Av. kutaka- "little, small."

A dwarf spheroidal galaxy of faint luminosity that is a member of the Local Group.

→ Ursa Minor; → system.

An annual → meteor shower whose → radiant lies in the constellation → Ursa Minor and is active between December 17 and December 24. The shower usually peaks around December 23.

→ Ursa Minor; → -ids.

An → impact cratrer on → Ceres which is the third largest crater on this → dwarf planet. Urvara is located south of → Occator and is about 160 km wide and 6 km deep. It has a prominent central peak that is about 3 km high.

Named for the ancient Indo-Iranian personification of fertility, Av. urvarā- "plant," often defied, Skt. urvárā- "land, soil, fertile field."

A person who uses or exploits something, such as a computer.

From use; M.E. usen from O.Fr. user "to use, employ," from V.L. *usare "to use," from L. uti "to use."

Kârbar "user," from bé kâr bordan "to use."

A committee whose members represent the astronomers who use the facilities of an observatory and which is intended to improve the interaction between the observatory and the users.

→ user; committee, M.E., from O.Fr. commettre "to commit," from L. committere "to bring together," from → com- + mittere "to put, send."

Komité, loan from Fr.; kârbarân plural of kârbar→ user.

1) Of, relating to, or in the interests of utility.
2) Of, characterized by, or adhering to → utilitarianism.

Coined by Jeremy Bentham (1748-1832) from → utility + -arian.

Philosophy: A doctrine according to which the virtue of a thing or an action is determined by its utility. The goal of utilitarian ethics is to promote the greatest happiness for the greatest number of people. The founders of this philosophical school were Jeremy Bentham (1748-1832) and James Mill (1773-1836).

→ utilitarian; → -ism.

1) The state or quality of being useful; usefulness.
2) Having, or made for, useful practical purposes. → utility software.

M.E. utilite, from O.Fr. utilite "usefulness," earlier utilitet, from L. utilitatem "usefulness, profit," from utilis "usable," from uti "to use."

Hudemandi, from hudemand "utile," from hudé "use" (as in bihudé "useless, vain, absurd"), from Mid.Pers. hudâg "good, useful, beneficent;" Av. hūdā- "doing good, producing wealth," from hū-, hu-, → eu-, + Av./O.pers. dā- "to give, grant, put," dadāiti "he gives;" Mid.Pers./Mod.Pers. dâdan "to give, put" (cf. Skt. dadáti "he gives;" Gk. tithenai "to place, put, set," didomi "I give;" L. dare "to give, offer;" Rus. delat' "to do;" O.H.G. tuon, Ger. tun, O.E. don "to do;" PIE base *dhe- "to put, to do") + -mand(i)

A part of the system software designed to support the operation of application software and is used to manage the computer files. Examples of utility software are disk diagnosis program, backup software, password generation software, and virus protection software. Also called utilities.

→ utility; → software.

The act or process of utilizing.

Verbal noun of → utilize.