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

The four largest and brightest satellites of → Jupiter, that is: → Io (Jupiter I), → Europa, → Ganymede, and → Callisto.

Galileo, who had discovered them, called them Sidera Medicæa "Medicean Stars" in honor of the Medici family. → Galilean Moons; → satellite.

The method of relating a measurement in one → reference frame to another moving with a constant velocity with respect to the first within the → Newtonian mechanics. The Galilean transformation between the coordinate systems (x,y,z,t) and (x',y',z',t') is expressed by the relations: x' = x - vt, y' = y, z' = z. Galilean transformations break down at high velocities and for electromagnetic phenomena and is superseded by the → Lorentz transformations.

→ Galilean; → transformation.

A space mission whose main goal was to explore → Jupiter and its moons and rings. The spacecraft was launched on October 19, 1989, arrived at Jupiter in December 1995. It disappeared on September 21, 2003, after eight years orbiting Jupiter, when mission controllers crashed it into → Jupiter's atmosphere. On December 7, 1995, Galileo's probe dived into Jupiter's atmosphere, and measured atmospheric pressure, density, and composition, and explored the planet's → radiation belts. Galileo had two parts: an orbiter and a descent probe that parachuted into Jupiter's atmosphere. The orbiter sent back hundreds of pictures of the four large → Galilean satellites of Jupiter (→ Io, → Europa, → Ganymede, and → Callisto). It made many discoveries during its eight years looping around Jupiter. It found evidence for layers of salt water below the surface on Europa, Ganymede, and Callisto, and measured high levels of volcanic activity on Io. When → Shoemaker-Levy slammed into Jupiter in 1994, Galileo had the only direct view of the → comet striking Jupiter's atmosphere. Galileo determined that → Jupiter's rings are formed from dust hurled up by → meteorite impacts on planet's inner moons. Measurements by the orbiter's → magnetometer revealed that Io, Europa, and Ganymede have metallic cores, while Callisto does not. Also, Galileo discovered that Ganymede possesses its own → magnetic field; it is the first moon known to do so. The orbiter also found that the Galilean satellites all have thin atmospheres. During it's trip from Earth to Jupiter, Galileo passed by and studied two asteroids: → Gaspra in 1991 and → Ida in 1993, around which it discovered → Dactyl, the first moon orbiting an asteroid (windows2universe.org).

→ Galileo; → mission.

In the absence of air resistance, any two bodies that are dropped from rest at the same moment will reach the ground at the same time regardless of their mass.

Galileo (1564-1642) was the first to determine, at the start of the seventeenth century, the law of constant acceleration of free-falling bodies. → law; → fall; → body.

An electrolytic cell capable of producing electric energy by electrochemical reaction.

→ galvanism; → cell.

A pair of dissimilar conductors, commonly metals, in electrical contact.

→ galvanism; → couple.

The direct electric current that flows between metals or conductive nonmetals in a → galvanic couple.

→ galvanism; → current.

1) The production of electricity from a chemical reaction.
2) The therapeutic application of electricity to the human body.

From Fr. galvanisme, after Luigi Galvani (1737-1798), the Italian physiologist, who demonstrated (1790) muscular action due to contact with dissimilar metals.

The coating of steel or iron with → zinc, either by immersion in a bath of molten zinc or by electrolytic deposition from a solution of zinc sulfate, to give protection against corrosion.

Verbal noun of → galvanize.

1) To coat a metal with → zinc by dipping into molten zinc or by electrolytic deposition.
2) To stimulate by application of an electric current.

From Fr. galvaniser, from galvanisme, → galvanism.

Gâlvânidan, from Gâlvâni, → galvanism, + -idan, → -ize.

A prefix denoting galvanic or galvanism in compound words, such as → galvanometer, → galvanoplasty.

Galvano-, from → galvanism.

An instrument for measuring or detecting small → direct currents, usually by the mechanical reaction between the magnetic field of the current and that of a magnet.

→ galvano- + → -meter.

A process used for covering an object with a thin layer of metal by electrochemical means.

→ galvano- + -plasty a suffix meaning "molding, formation, surgical repair, plastic surgery," from Gk. -plastia, from plastos "molded, formed," from plassein "to mold."

Gâlvânopuši, from gâlvâno-, → galvano-, + puši "covering, coating," from pušidan "to cover; to put on" (Mid.Pers. pôšidan, pôš- "to cover; to wear;" cf. Mid.Pers. pôst; Mod.Pers. pust "skin, hide;" O.Pers. pavastā- "thin clay envelope used to protect unbaked clay tablets;" Skt. pavásta- "cover," Proto-Indo-Iranian *pauastā- "cloth").

1) An amusement or pastime.
2) The material or equipment used in playing certain games.
3) A competitive activity involving skill, chance, or endurance on the part of two or more persons who play according to a set of rules, usually for their own amusement or for that of spectators (Dictionary.com).

M.E. gamen. O.E. gaman "game, joy, fun, amusement;" cf. O.Fris. game "joy, glee," O.N. gaman, O.H.G. gaman "sport, merriment," D. gamen, Sw. gamman.

Bâzi, from Mid.Pers. wâzig "game, play," related to bâzidan "to play," bâxtan/bâz- "to loose (in game);" Proto-Ir. *uāz- "to play, contend;" cf. Skt. vāja- "contest, war, gain, reward" (Cheung 2007).

1) The third letter of the Greek alphabet (γ, Γ).
2) Symbol used to denote the ratio of the principal specific heats C_P/C_V of a gas, where C_P is the specific heat at constant pressure and C_V that measured at constant volume.
3) Unit of magnetic field intensity, equal to 10^-5 gauss.
4) The distance of the Moon's shadow axis from Earth's center in units of equatorial Earth radii. It is defined at the instant of → greatest eclipse when its absolute value is at a minimum (F. Espenak, NASA).

The third letter of the Gk. alphabet, from Gk. gamma, from Phoenician gimel.

A bright, third → magnitude (3.22) → giant star of → spectral type K1, also called → Errai, HR 8974, HIP 116727, and HD 222404. γCephei has a → surface temperature of 4920 K a mass of 1.40 Msun, a → luminosity 10.6 solar, and a radius 4.8 solar. Its distance is estimated to be 45 → light-years. γ Cephei will become the → Pole Star in about 2,000 years. γ Cephei has a low mass → companion (B), a main → main sequence star of spectral type M4 V with a mass of 0.4 Msun. It orbits the → primary star every 67.5 years. An → extrasolar planet. (γ Cephe b) has been discovered orbiting the main star.

Gamma, as in → Bayer designation; → Cepheus.

The star → Sadr.

Gk. letter → gamma; Cygni, genitive of → Cygnus.

A type of → radioactivity in which some unstable atomic nuclei dissipate excess energy by a spontaneous electromagnetic process, usually accompanied by → alpha decay or → beta decay.

→ gamma; → decay.

A process which reinforces the → kappa mechanism in a → partial ionization zone. Because the temperature in the partial ionization zone is lower than in the adjacent stellar layers, heat tends to flow into the zone during compression, prompting further ionization.

γ, after the smaller ratio of → specific heats caused by the increased values of C_p and C_v; → mechanism.

An → electromagnetic wave with a typical → wavelength less than 10^-2Å (10^-12 m), corresponding to frequencies above 10¹⁹ Hz and photon energies above 100 → keV.

→ gamma; → ray.