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

1) The Water Serpent. The longest and largest constellation in the sky, stretching almost 7 hours of right ascension, and covering over 1300 square degrees, from → Canis Minor to → Libra. It lies south of → Cancer, → Leo, and → Virgo, and is best seen in the northern hemisphere during the months of February through May. Its brightest star is → Alphard. Abbreviation: Hya; Genitive: Hydrae.
2) The third satellite of → Pluto discovered in 2005 by astronomers using the → Hubble Space Telescope images. Also called Pluto III (P3). It has an estimated diameter of between 60 and 170 km and an → orbital period of 38.2 days. It orbits the → barycenter of the → Pluto-→ Charon system at a distance of about 65,000 km.

Hydra, from L. hydrus, from Gk. hydra "water-snake;" cf. Av. udra- "otter;" Skt. udrá- "otter;" O.H.G. ottar "otter;" O.E. otor, ottor; Ger. Otter; E. otter; Lith. udras, udra "otter;" akin to → water. In Gk. mythology, this constellation represents the gigantic nine-head water-snake which haunted the swamps of Lerna. Herakles was sent to destroy her as one of his twelve labours, but for each of her heads that he decapitated, two more sprang forth. So with the help of Iolaos, Herakles applied burning brands to the severed stumps, cauterizing the wounds and preventing regeneration. In the battle he also crushed a giant crab (→ Cancer) beneath his heel which had come to assist Hydra.

Hudrâ, from Gk. hydra, as above. → Hydrus (آبمار)

A relatively poor → galaxy cluster at about 50 Mpc containing a pair of bright galaxies near its centre: NGC 3309 and NGC 3311. Also known as Abell 1060 (→ Abell catalog), Hydra I is the prototype of an evolved and dynamically relaxed cluster, being dominated by early-type galaxies and having a regular core shape.

→ Hydra; → cluster.

To combine chemically with → water.

From → hydr-, → hydro- + -ate a verbal suffix.

Hidridan, from Gk. → hydr-, âbidan, from âb, → water, + -idan infinitive suffix.

Combined with → water molecules.

P.p./adj. of → hydrate.

The process of combining with → water.

Verbal noun of → hydrate.

Operated, moved, or employing water or other liquids in motion.

From Gk. hydraulikos organon "water organ," from → hydro- "water" + aulos "musical instrument, hollow tube."

A device, which uses the energy of water flowing by gravity intermittently through a pipe to force a small portion of the water to a height greater than that of the source.

→ hydraulic; → ram.

A binary compound containing hydrogen and another element, such as CH, OH, and HCl.

→ hydr- + -ide.

Hidrur, loan from Fr.

A combining form (hydr- before a vowel) originally meaning "water," but also "liquid, gas." In chemical nomenclature, often denotes a compound of hydrogen.

Gk. hydro-, combining form of hydor "water," cognate with Skt. udá- "water;" Khotanese ūtcā "water;" Hittite uātar; L. unda "wave;" O.C.S., Rus. voda; Lith. vanduo; P.Gmc. *watar (cf. Du. water; O.H.G. wazzar; Ger. Wasser; Goth. wato; O.E. wæter; E. water); from PIE base *wed- "water; wet."

Hidro-, loanword from Gk., as above. Âb- "water," from 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."

Any of a class of compounds containing only → hydrogen and → carbon. Hydrocarbons are organic compounds found in coal, petroleum, natural gas, and plant life. They are used as fuels, solvents, and as raw materials for numerous products such as dyes, pesticides, and plastics. Petroleum is a mixture of several hydrocarbons.

→ hydro- + → carbon.

Same as → hydrogen cyanide.

→ hydro-; → cyano-; → acid.

Of or pertaining to → hydrodynamics.

→ hydro- + → dynamic.

Fluid mechanics: A → partial differential equation which describes the motion of an element of fluid subjected to different forces such as pressure, gravity, and frictions.

→ hydrodynamic; → equation.

The state of a star when all its internal forces are in equilibrium. The main forces are gas pressure, radiation pressure due to thermonuclear fusion that tends to disrupt the star, and the opposing gravity. → hydrostatic equilibrium.

→ hydrodynamic; → equilibrium.

The branch of physics dealing with the motion, energy, and pressure of neutral → fluids.

→ hydro- + → dynamics.

The most abundant → chemical element in the Universe. Symbol H; → atomic number 1; → atomic weight 1.00794; → melting point -259.14°C; → boiling point -252.87°C. It was discovered by the English physicist Henry Cavendish in 1766, who called it the "inflammable air."
See also:
→ antihydrogen, → atomic hydrogen, → heavy hydrogen, → hydrogen bond, → hydrogen burning, → hydrogen coma, → hydrogen cyanide, → hydrogen fusion, → hydrogen ion, → hydrogen line, → hydrogen shell burning, → hydrogenate, → hydrogenation, → hydrogenize, → ionized hydrogen region, → metallic hydrogen, → molecular hydrogen, → neutral hydrogen, → orthohydrogen, → parahydrogen, → triatomic hydrogen molecular ion.

Hydrogen, from Fr. hydrogène, from Gk. hydro-, combining form of hydor "water" → hydro- + Fr. -gène "producing," → -gen; coined in 1787 by the French chemist Guyton de Morveau (1737-1816) because it forms water when exposed to oxygen.

The attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. Usually the electronegative atom is oxygen, nitrogen, or fluorine, which has a partial negative charge. The hydrogen then has the partial positive charge.

→ hydrogen; → bond.

→ proton-proton chain.

→ hydrogen; → burning.

The cometary cloud of hydrogen, detectable in ultraviolet light, that is immensely bigger than even the huge visible coma it surrounds. It is produced by the dissociation of water into hydrogen and oxygen and by other processes set into motion by solar radiation and and the solar wind.

→ hydrogen, → coma.

A colorless or light blue liquid or gas, a triatomic cyanide, which is extremely flammable. HCN is an important industrial chemical and over a million tonnes are produced yearly in the world. It is produced industrially by reacting methane and ammonia in air at high temperature. A wide range of combustion processes produce HCN gas in the smoke or fumes. HCN is found naturally throughout the environment at low levels as it is released from volcanoes and certain plants and bacteria. Hydrogen cyanide is abundant in all kinds of astronomical environments, from dark clouds to star-forming regions and circumstellar envelopes. The first detection of interstellar HCN (at 88.6 GHz) and H¹³N (at 86.3 GHz) was reported by Buhl & Snyder (1971, ApJ 163, L47). Also called → hydrocyanic acid and → prussic acid.

→ hydrogen; → cyanide.