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

An → H II region, a → planetary nebula, or a → supernova remnant.

→ gaseous; → nebula.

Gases responsible for the greenhouse effect. These gases include: water vapor (H₂O), carbon dioxide (CO₂); methane (CH₄); nitrous oxide (N₂O); chlorofluorocarbons (CF_xCl_x); and tropospheric ozone (O₃).

→ greenhouse; → gas.

The → Greenwich Mean Sidereal Time corrected for → nutation. Therefore, it is measured with respect to the → true vernal equinox. GAST and GMST differ by the → equation of the equinoxes.

→ Greenwich Meridian; → apparent; → sidereal; → time.

Theoretical gas assumed to consist of perfectly elastic molecules of negligible volume and mutual attraction force. Also called → perfect gas.

→ ideal; → gas.

An → equation of state that relates pressure (P), temperature (T), and volume (V) of an ideal or → perfect gas: PV = nRT, where n is the number of → moles of gas present and R is the → universal gas constant. Equivalently: PV = NkT, where N is the number of atoms of gas present and k is → Boltzmann's constant.

→ ideal; → gas; → law.

Any one of six gases helium, neon, argon, krypton, xenon, and radon, all of whose atomic shells contain complete numbers of electrons so that the atoms are almost completely chemically inactive. Same as noble gases.

→ inert; → gas.

Electrically charged particles of the solar wind and gas liberated from comets within the solar system.

→ interplanetary; → gas.

Gas, mostly hydrogen, in the interstellar space found in a variety of forms: molecular, atomic, ionized, plasma.

→ interstellar; → gas.

A gas composed partially or totally of → ions.

→ ionized; → gas.

A theory that explains macroscopic properties of gases, such as pressure, temperature, or volume, by considering their molecular composition and motion.

→ kinetic; → theory; → gas.

A blue star of visual magnitude 2.49, the brightest in the constellation → Pegasus. Markab is a relatively hot star of → spectral type B9, with a total luminosity about 200 times that of the Sun, a surface temperature of about 11,000 K, and a radius 4.3 times solar lying 140 light-years away.

Markab seems to be a corruption of Mankab in the original Ar. name of this star Mankib al-faras (منکب‌الفرس) "the horse's shoulder," from mankib "shoulder" + faras "horse," referring to Pegasus in Gk. mythology.

Same as → Dyson sphere.

→ mega-; → structure.

A gas which is not ionized.

→ neutral; → gas.

A gaseous chemical element that does not readily enter into chemical combination with other elements. Examples are helium, argon, krypton, xenon, and radon. Same as → inert gas.

Noble, from O.Fr. noble, from L. nobilis "well-known, famous, of superior birth," earlier gnobilis, literally "knowable," from gnoscere "to come to know" (Fr. connaître; Sp. conocer); cognate with Pers. šenâxtan "to know, discern, distinguish, be acquainted with;" Mid.Pers. šnâxtan, šnâs- "to know, recognize," dânistan "to know;" O.Pers./Av. xšnā- "to know, learn, come to know, recognize;" cf. Skt. jñā- "to recognize, know," jānāti "he knows;" Gk. gignoskein "to know, think, judge;" P.Gmc. *knoeanan; O.E. cnawan; E. know; Rus. znat "to know;" PIE base *gno- "to know;" → gas.

Gâz, → gas; huped "noble," from Mid.Pers. hupid "noble," from hu- "good, well" (Mid.Pers. hu-; O.Pers. ^hu- "good, well" (ukāra- "having good people"); Av. hu-, hū- "well, good, beautiful" (hu-kərp- "well-shapen," hūxta- "well spoken," hu-manah- "good-minded"); cf. Skt. su- "good" (svasti "well-being, good luck," sumánas- "good-minded," sūktá- "well spoken"); L. from Gk. eu "well," combining form of eus "good" (hu-gies "healthy"); Gallic su-; O.S. su-; Welsh hy-; PIE base *su-) + pid "father," variant of pidar; Mod.Pers. pedar "father" (O.Pers. pitā- "father;" Av. patar-; Skt. pitár-; Gk. pater; L. pater, O.H.G. fater).

1) General: The slow release of a gas that was trapped, frozen, absorbed or adsorbed in some material.
2) Planets: Release of the gases locked in the interior of a planet during volcanic activity so that they become part of the planet's atmosphere.

→ out + verbal noun from → gas.

The Winged Horse. A large constellation in the northern hemisphere at 22h 50m right ascension, 20° north declination. The stars → Markab, → Scheat, and → Algenib form three corners of the famous Great → Square of Pegasus, which is completed by the star → Alpheratz from neighboring → Andromeda. Abbreviation: Peg; Genitive: Pegasi.

In Gk. mythology, Pegasus is the winged horse that was fathered by Poseidon with Medusa. When the head of Medusa was cut off by Perseus, the horse sprang forth from her pregnant body. Pegasus aided Perseus in his fight against both the Chimera and the Amazons.

Pegâsus, from Gk., as above; asb-e bâldâr "Winged Horse," referring to the Gk. mythology, from asb→ horse; bâl, → wing; dâr "having, possessor" (from dâštan "to have, to possess," Mid.Pers. dâštan, O.Pers./Av. root dar- "to hold, keep back, maintain, keep in mind," Skt. dhr-, dharma- "law," Gk. thronos "elevated seat, throne," L. firmus "firm, stable," Lith. daryti "to make," PIE *dher- "to hold, support").

A hypothetical gas with molecules of negligible size that exert no intermolecular forces. Also called → ideal gas.

→ perfect; → gas.

Gas which cannot be liquefied by pressure alone; gas above its critical temperature.

→ permanent; → gas.

→ Electromagnetic radiation in equilibrium in a → black body cavity. Photons can be treated as the simplest → ideal gas because all the particles move at the same velocity, the → speed of light. There are, nevertheless, two main differences. 1) Photons are → bosons and → Bose-Einstein statistics must be used. However, photons do not interact with each others so that no approximation is made by neglecting inter-particle forces. 2) Some photons scatter off the walls, with some being absorbed and new ones being emitted continually; so that no constraint can be placed on their number.

→ photon; → gas.

A gas capable of undergoing a → polytropic process.

→ polytropic; → gas.