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

A theoretical frequency distribution for a set of variable data, usually represented by a bell-shaped curve with a mean at the center of the curve and tail widths proportional to the standard deviation of the data about the mean.

→ Gaussian; → distribution.

A method of solving a matrix equation of the form A x = b, where A is a matrix and x and b are vectors. The process consists of two steps, first reducing the elements below the diagonal to 0 and second, back substituting to find the solutions.

→ Gaussian; → elimination.

The function e^-x2, whose integral in the interval -∞ to +∞ gives the → square root of the → number pi: ∫e^-x2dx = √π. It is the function that describes the → normal distribution.

→ Gaussian; → function.

The constant, denoted k, defining the astronomical system of units of length (→ astronomical unit), mass (→ solar mass), and time (→ day), by means of → Kepler's third law. The dimensions of k² are those of Newton's constant of gravitation: L ³M ^-1T ^-2. Its value is: k = 0.01720209895.

→ Gaussian; → gravitational; → constant.

A → complex number whose → real and → imaginary parts are both integers.

→ Gaussian; → integer.

The shape of a curve representing a normal distribution.

→ Gaussian; → profile.

Math.: The condition of having → Gaussian distribution. The extent to which something is Gaussian.

→ Gaussian + → -ity.

1) Law of combining volumes. The volumes of gases used and produced in a chemical reaction, are in the ratio of small whole numbers when measured at constant temperature and pressure.
2) For a gas held at constant volume, there is a direct correlation between temperature and pressure: P₁/T₁ = P₂/T₂. Gay-Lussac's law, → Boyle-Mariotte law, and → Charles' law were later unified into the → ideal gas law.

Named after Joseph Louis Gay-Lussac (1778-1850), a French chemist and physicist; → law.

A follow-up community network concerned with → gamma-ray burst (GRB)s. It deals with: 1) locations of GRBs and other → transients detected by spacecraft (most in real-time while the GRB is still bursting), and 2) reports of follow-up observations (the Circulars) made by ground-based and space-based optical, radio, X-ray, TeV, and other observers. The GCN Circulars allow the GRB follow-up community to make optimum use of its limited resources (labor and telescope time) by communicating what has already been done or will soon be done.

→ gamma ray; → coordinate; → network.

The prototype of the → L dwarf class. It has a spectral type of L4 V. This object was discovered by Becklin & Zuckerman (1988, Nature 336, 656) as the red companion to a → white dwarf (DA4) lying 104 → light-years away. Its true nature was however recognized several years later (Kirkpatrick et al. 1993, ApJ 406, 701). It has an → effective temperature of 1900 K and a luminosity about 10^-4 times that of the Sun (→ solar luminosity).

GD, referring to Giclas Dwarf, a catalog of white dwarf stars compiled at the Lowell Observatory (Giclas et al. 1980, LowOB 8, 157).

A faint glow of light in the night sky seen exactly opposite the Sun. The gegenschein is sunlight back-scattered off millimeter-sized dust particles along the ecliptic. In comparison with zodiacal light (forward-scattered sunlight), which is triangular in shape and found near the horizon, the gegenschein is roughly circular. Same as counterglow.

Gegenschein, from Ger. gegen "counter, opposed to" (O.H.G. gegin, gagan, M.Du. jeghen, E. against, again) + Schein "glow, shine" (M.H.G. schinen, O.H.G. skinan, P.Gmc. *skinanan; E. shine; cf. Mod.Pers. sâyé "shadow;" Mid.Pers. sâyak "shadow;" Av. a-saya- "throwing no shadow;" Skt. chāya- "shadow;" Gk. skia "shade;" Rus. sijat' "to shine;" PIE base *skai- "bright").

Pâdfrouq "counterglow," from pâd- "agaist, contrary to" (from Mid.Pers. pât-; O.Pers. paity "agaist, back, opposite to, toward, face to face, in front of;" Av. paiti; cf. Skt. práti "toward, against, again, back, in return, opposite;" Pali pati-; Gk. proti, pros "face to face with, toward, in addition to, near;" PIE *proti) + foruq "light, brightness" (related to rôšan "light; bright, luminous;" ruz "day," afruxtan "to light, kindle;" Mid.Pers. payrog "light, brightness," rošn light; bright," rôc "day;" O.Pers. raucah-; Av. raocana- "bright, shining, radiant," raocah- "light, luminous; daylight;" cf. Skt. rocaná- "bright, shining, roka- "brightness, light;" Gk. leukos "white, clear;" L. lux "light" (also lumen, luna; E. light, Ger. Licht, and Fr. lumière; PIE base *leuk- "light, brightness").

A device for detecting ionizing radiations, whether corpuscular (α-, β-particles), or electromagnetic (X- and gamma-rays). It consists essentially of a fine wire anode (e.g., tungsten) surrounded by a coaxial cylindrical metal cathode, mounted in a glass envelope containing gas at low pressure. A large potential difference (800 to 2000 volts) is maintained between the anode and the cathode. The ionizing particle can enter through a thin glass or mica window. The particle produces ionization of gas molecules. The ions are accelerated by the electric field and produce more ions by collisions, causing the ionization current to build up rapidly. The current, however, decays quickly since the circuit has a small time constant. There is therefore a momentary potential surge which may be amplified and made to actuate a relay to advance a mechanical counter, or to produce a click in a loudspeaker. Same as Geiger-Mulle counter.

Named after Hans Geiger (1882-1945), the German physicist, who invented the instrument. He is also known for his work on atomic theory and cosmic rays; → counter.

To castrate (an animal, especially a horse).

M.E. gelden, from O.Norse gelda, ultimately from PIE *ghel- "to cut."

Axtan, variant of âxtan, âhixtan, âhiz- "to draw out; castrate, geld," → object.

A castrated male animal, especially a horse.

→ geld; → -ing.

A bright → gamma-ray source discovered in 1973 in the constellation → Gemini with instruments aboard NASA's first γ-ray satellite SAS-2. It was known only as a γ-ray source until it was detected in X-rays by the Einstein Observatory and associated with an optical counterpart of apparent magnitude 25. Because its luminosity outside of the γ-ray region is extremely low, the nature of this object remained a mystery until the discovery of pulsed emission, by the → ROSAT satellite in 1992, showed that it is a → pulsar. The pulsar period (~237 milliseconds) and its → period derivative (~1.1 × 10^-14 s s^-1) correspond to a → spin-down age of ~340,000 years. Also called PSR J0633+1746 (see Bignami & Caraveo 1996, ARA&A 34, 331 for a review).

An abbreviation for the Gemini gamma ray source. More amusingly, Geminga has been related to the Italian dialectal ghè minga spoken by the involved astronomers. This, in Milanese, means "it's not there," referring to the fact that the source could not be detected in the radio frequencies, one of the ongoing enigmas.

The Twins. A prominent constellation of the northern hemisphere and the third (and northernmost) of the → Zodiac. It lies south and east of → Auriga, west of → Cancer, and north and east of → Orion, at 7h right ascension and +22° declination. Its brightest stars are → Castor and → Pollux. Abbreviation: Gem; genitive: Geminorum.

Gemini, from M.E., from L. gemini, plural of geminus "twin; double;" cf. Av. yəma- "twin;" Skt. yamá-, yamala- "twin, paired;" Persian dialects Kermâni jomoli "twin," Qâyeni jamal "twin," Tabari da-cembali "twin;" PIE base *iem- "to hold."

Dopeykar, from do "two" (Mid.Pers. do, Av. dva-; Skt. dvi-; Gk. duo; L. duo ( Fr. deux); E. two; Ger. zwei) + peykar "figure, form, body" (from Mid.Pers. pahikar "picture, image;" from O.Pers. patikara- "picture, (sculpted) likeness," from patiy "against" (Av. paiti; Skt. prati; Gk. poti/proti) + kara- "doer, maker," from kar- "to do, make, build;" Av. kar-; Skr. kr-; cf. Skt. pratikrti- "an image, likeness, model; counterpart").

A → meteor shower that occurs in the first half of December, with its → radiant in the → constellation → Gemini. Geminids are pieces of debris from the extinct comet → 3200 Phaethon. The shower appears when Earth runs into a stream of the debris every year in mid-December, causing → meteors to fly from that constellation.

→ Gemini + → -ids.

The brightest star in the constellation → Corona Borealis. Same as → Alphekka.

Gemma, from L. gemma "precious stone, jewel," originally "bud," from the root *gen- "to produce", → generate.

Alfakké, → Alphekka.

In some languages (not in English, nor in Persian) a set of two or more grammatical categories (called → masculine, → feminine, and → neuter) into which nouns, pronouns, and adjectives are divided. For example, French, Spanish, and Italian have two genders, masculine and feminine (shown, for example, in French by the use of le and la, respectively); German and Russian have three genders, masculine, feminine, and neuter. Ancient Iranian languages had three genders, like Sanskrit and Greek.

From M.E. gendre, from O.Fr. gendre, from stem of L. genus "race, stock, family; kind, rank, order; species."

Žâné "race, species," ultimately from Proto-Ir. *zan- "to be born," cf. Av. za(n)- "to give birth; to be born;" related to Pers. zâdan, akin to L. genus, as above, → generate; the transformation of z into ž, as in nežâd, → race.

The basic unit of hereditary that is an ordered sequence of nucleotides located in a particular position of a particular chromosome. It is the means by which characteristics are transmitted from parents to offsprings.

From Ger. Gen, coined 1905 by Danish scientist Wilhelm Ludvig Johannsen (1857-1927), from Gk. genos "race, kind," genesis "origin," genea "generation, race;" cognate with L. genus "race, stock;" generare "to bring forth;" Pers. zâdan "to bring forth;" → generate.

Žen, loanword from Fr., as above.