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CD School House 9.0 - Wayzata Technology (1994).iso
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descrip.dat
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orbit), we see the planet nearly fully illuminated, but because of
its distance it appears small. As Venus moves closer to earth, the phase
decreases (we see less of the illuminated portion of the planet). It takes
Venus several months to move from one of these extremes to the other.
$
EARTH
The earth (Terra) has a substantial atmosphere, mainly of nitrogen and oxygen,
and a magnetosphere linked to a magnetic field. Two-thirds of the planet is
covered by water. On average the earth's surface transfers to the atmosphere
an amount of energy equal to that it absorbs.
The earth consists of three main internal layers: the crust, mantle, and core.
The crust consists largely of sedimentary rocks, such as limestone and
sandstone, resting on a base of igneous rocks, such as granite and basalt. The
mantle's composition is thought to contain a high proportion of silicate rocks.
The core is composed predominantly of iron with several, possibly many,
additional components.
It is believed that the pressure at the earth's center is about 400
gigapascals, whereas the internal temperature may exceed 5 000 K at the center.