An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 634
early-type galaxy (ETG)
  کهکشان ِ گونه‌ی ِ آغازین   
kahkešân-e gune-ye âqâzin

Fr.: galaxie de type précoce   

In the → Hubble classification, galaxies on the left part of the → Hubble sequence. Early-type galaxies tend to have redder colors, higher average surface brightnesses, and lower → neutral hydrogen content than → late-type galaxies. This terminology is based on the obsolete and erroneous idea that → elliptical and → lenticular galaxies might be evolutionary precursors to → spiral and → barred spiral galaxies.

early; → type; → galaxy.

early-type star
  ستاره‌ی ِ گونه‌ی ِ آغازین   
setâre-ye gun-ye âqâzin (#)

Fr.: étoile de type précoce   

Hot, luminous stars of → spectral type O, B, A, and F0 to F5. They were originally thought, wrongly, to be at an earlier stage of evolution than → late-type stars. See also → spectral classification.

early; → type; → star.

zamin (#)

Fr.: terre   

The third planet from the Sun. At → perihelion, it is 147,099,590 km from the Sun, and at → aphelion it is 152,096.150 km, whereas its mean distance from the Sun (→ astronomical unit) is 149,598 × 106 km. Its orbital period is 365.2563 days (→ sidereal year) and its → eccentricity 0.017. Other characteristics: → axial inclination 23.44°; rotation period 23.934 h (→ sidereal day); mean density 5.52 g/cm3; mass 5.974 × 1024 kg; → escape velocity 11.18 km/s; average → albedo 0.37.
The Earth's atmosphere consists of 78% nitrogen, 21% oxygen and 0.9% argon, plus carbon dioxide, hydrogen, and other gases in much smaller quantities. The atmospheric pressure at sea level is about 1,000 mbar. The surface average temperature is 15° C, but it varies, on the average, between -50° C (winter, Siberia) and up to + 40° C (summer, Sahara).
Liquid water covers 71% of the surface. Over 5,000 active volcanoes have been registered throughout man's known history. The outer layer of the planet, the → lithosphere, is covered with the → crust. In the → upper mantle and beneath the lithosphere, lies → asthenosphere. Convection in the asthenosphere has caused → plate tectonics motions and continent drifts. The densest layer of the Earth is its → core, about 3000 km to 6400 km beneath the surface, consisting primarily of iron and nickel. This core is believed to be at the origin of the magnetic field, which reaches about 3 × 10-5 tesla near the equator. It has only one natural satellite, the Moon (M.S.: SDE).

M.E. erthe, from O.E. eorðe "ground, soil, dry land;" cf. O.N. jörð, M.Du. eerde, O.H.G. erda, Goth. airþa; from PIE base *er-.

Zamin, variant zami "earth, floor, land," Mid.Pers. zamig, Av. zam- "the earth;" cf. Skt. ksam- "the ground, earth;" Gk. khthôn, khamai "on the ground;" L. homo "earthly being" (as in homo sapiens, homicide, humble, humus, exhume), humus "the earth;" O.Russ. zemi "land, earth;" PIE root *dh(e)ghom "earth".

Earth mass
  جرم ِ زمین   
jerm-e zamin (#)

Fr.: masse de la Terre   

The mass of our planet Earth, which is 5.9736 × 1024 kg, 317.83 times smaller than the → Jupiter mass. The Earth mass is in particular used to describe the mass of → super-Earth  → extrasolar planets.

Earth; → mass.

Earth radius
  شعاع ِ زمین   
šo'â'-e zamin (#)

Fr.: rayon terrestre   

The distance from the Earth's center to its surface, about 6,371 km.

earth; → radius.

Earth's core
  مغزه‌ی ِ زمین   
maqze-ye Zamin

Fr.: noyau terrestre   

The innermost part of the Earth consisting of a solid → inner core, mainly composed of → iron, and a → liquid → outer core. The → pressure and → temperature are so extreme that the molten iron solidifies. The temperature at the inner core boundary is expected to be close to the → melting point of iron at 330 gigapascal (GPa). From static laser-heated diamond anvil cell experiments up to 200 GPa, using synchrotron-based fast → X-ray diffraction as a primary melting diagnostic, S. Anzellini et al. (2013, Science 340, 484) conclude that the melting temperature of iron at the inner core boundary is 6230 ± 500 K. This estimation favors a high heat flux at the core-mantle boundary with a possible partial melting of the → mantle. The inner core, 2,400 km in diameter, is suspended in the molten metal of the → outer core, which is about 2,240 km thick. The temperature difference between the mantle and the core is the main engine for large-scale thermal movements, which coupled with the → Earth's rotation, function as a generator for the planet's → magnetic field.

Earth; → core.

Earth's crust
  پوسته‌ی ِ زمین   
puste-ye Zamin (#)

Fr.: croûte terrestre   

The rocky outermost layer of the Earth, ranging from about 10 to 65 km in thickness. It is distinguished from the underlying the → Earth's mantle layer by its more → silicon- and → aluminium-rich composition, lower density, and the lower velocity at which it conducts seismic energy. It includes → continental crust (about 40 km thick) and → oceanic crust (about 7 km thick). The crust and the topmost layer of the mantle form the → lithosphere. The five most abundant → chemical elements in the Earth's crust are, in percentage by weight of the Earth's crust: → oxygen (O) 46%, silicon (Si) 28%, aluminium (Al) 8%, → iron (Fe) 5%, and → calcium (Ca) 4%.

Earth; → crust.

Earth's mantle
  گوشته‌ی ِ زمین   
gušte-ye Zamin

Fr.: manteau terrestre   

A major subdivision of Earth's internal structure, located beneath the → Earth's crust and above the central → core. On average, the mantle begins 35 km below the surface and ends at a depth of about 2,900 km. See also → upper mantle and → lower mantle, → asthenosphere, → lithosphere.

Earth; → mantle.

Earth's rotation
  چرخش ِ زمین   
carxeš-e zamin (#)

Fr.: rotation de la Terre   

The natural motion of the Earth around its own axis, which takes place once in a → sidereal day. The Earth rotates toward the → east, in the same direction as it revolves around the Sun. If viewed from the north celestial pole, the Earth turns → counterclockwise. The opposite is true when the Earth is viewed from the south celestial pole. The Earth's rotation is responsible for the diurnal cycles of day and night, and also causes the apparent movement of the Sun across the sky. The Earth's rotation velocity at the → equator is 1,673 km h-1 or about 465 m s-1. More generally, at the → latitude  φ it is given by: vφ = veq cos φ, where veq is the rotation velocity at the equator. The Earth's rotation is gradually slowing down under the action of the → tides, which are generated by the → gravitational attraction of the → Moon. As the result of this → tidal friction, the day is becoming longer at a rate of about 2 milliseconds, or 0.002 seconds, per century (or one second every 50,000 years). Moreover, the loss of the Earth's → rotational angular momentum increases the Moon's → orbital angular momentum, because the angular momentum of the → Earth-Moon system is conserved. In consequence, the Moon slowly recedes from the Earth by about 4 cm per year, which leads to increasing its orbital period and the length of a month as well.

Earth; → rotation.


Fr.: astéroide croiseur, comète ~   

An → asteroid or → comet whose → orbit occasionally brings it relatively close to the Earth. → near-Earth object.

Earth; → grazer.

Earth-Moon system
  راژمان ِ زمین-ماه   
râžmân-e Zamin-Mâh

Fr.: système Terre-Lune   

A physical system composed on the → Earth and the → Moon in which both objects directly influence each other. The total energy in the Earth-Moon system is conserved. The most notable influence that the two objects have on each other is → tides.
See also: → tidal braking, → tidal bulge, → tidal capture, → tidal coupling, → tidal disruption, → tidal force, → tidal friction, → tidal heating, → tidal locking, → tidal radius, → tidal stretching.

Earth; → Moon; → system.

zamin-tâb (#)

Fr.: lumière cendrée   

The illumination of the dark part of the Moon's disk by the light reflected from the Earth's surface and atmosphere. Also called → earthshine.

earth; → light.

zaminlarzé (#)

Fr.: tremblement de terre   

Sudden shaking of the → Earth's surface caused by the passage of a → seismic wave whose mechanical effects can be destructive. See also → starquake.

earth; → quake.

zamin-tâb (#)

Fr.: lumière cendrée   

The visibility of that part of the Moon not illuminated by the Sun. The phenomenon is caused by the solar light reflected by the Earth. It was explained correctly for the first time by Leonardo da Vinci (M.S.: SDE). Same as → earthlight.

earth; → shine.

xâvar (#)

Fr.: est   

The point on the → celestial horizon 90° → clockwise from the → north point. The point where the Sun rises at the → equinoxes.

O.E. east, from P.Gmc. *aus-to-, *austra- "east, toward the sunrise" (cf. Du. oost, Ger. Ost, O.N. austr "from the east"), from PIE *aus- "dawn" (cf. Av. uš-, ušah- "dawn," Skt. usas-, usah- "dawn," Gk. aurion "morning," Lith. auszra "dawn," L. aurora "dawn," auster "south").

Xâvar "east," originally "west," from Mid.Pers. *xvar barân "where the Sun is led," from xvar "sun" (Av. hū-, hvar- "sun", cf. Skt. surya-, Gk. helios, L. sol, O.H.G. sunna, Ger. Sonne, E. sun; PIE base *sawel- "sun") + barân, pr.p. of bar-, bordan "to carry, lead" (Mid.Pers. burdan, O.Pers./Av. bar- "to bear, carry," barəθre "to bear (infinitive)," Skt. bharati "he carries," Gk. pherein, L. fero "to carry;" PIE base *bher- "to carry") + time and place suffix -ân.

xâvari (#)

Fr.: est, de l'est, oriental   

Lying toward or situated in the east.

From → east + -ern an adjective suffix occurring with names of directions.

Xâvari from xâvar, → east, + -i adj. suffix.

eastern elongation
  درازش ِ خاوری   
derâzeš-e xâvari

Fr.: élongation est   

The position of a planet when it can be seen in the western sky just after sunset.

eastern; → elongation.

âsân (#)

Fr.: facile, aisé   

1) Not hard or difficult; requiring no great labor or effort.
2) Free from pain, discomfort, worry, or care (

M.E. aisie, esy, from O.Fr. aisie "comfortable, at ease, rich, well-off," p.p. of aisier "to put at ease," from aise "comfort, pleasure, well-being," of unknown origin.

Âsân "easy," from Mid.Pers. âsân "calm, quiet, at rest, peaceful, easy," related to âsudan "to rest, repose;" Av. ā- + saē- (saii-) "to lie down, go to sleep," → holiday.


Fr.: écouter de façon indiscrète   

To listen secretly to a private conversation.

Probably back-formation from → eavesdropper.

Gušârdan, from gušâr, → eavesdropper, + -dan infinitive suffix.

gušâr (#)

Fr.: écouteur   

A person or thing that secretly listens to or monitors the private conversation or data of others.

From M.E. eavesdrop, from O.E. yfesdrype "place around a house where the rainwater drips off the roof," literally "one who stands on the eavesdrop in order to listen to conversations inside the house," from eaves "the lower border of a roof that overhangs the wall" + drip, drop "to fall in small portions."

Gušâr in Tabari "eavesdropper," from guš, → ear, + -âr probably contraction of dâr (as in dustâr/dustdâr) agent noun from dâštan "to hold, have, possess; appoint, erect," → property.

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