An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 5 Search : Earth''s
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.

inclination of Earth's equator
  درکیل ِ هموگار ِ زمین   
darkil-e hamugâr-e zamin

Fr.: inclinaison de l'équateur terrestre   

obliquity of the ecliptic.

inclination; → Earth; → equator.