Page 112 - SST Class 06

times as far from the Sun as the Earth is and life. There is abundance of water in all its three
takes almost 12 years to travel around the Sun. states—liquid, solid and gaseous. Because three-

Saturn : Saturn is famous for its rings. The rings fourth of the Earth’s surface is covered by water,
were first observed (with a telescope) in 1610 by the Earth looks blue when seen from space. For
Galileo and are made up of huge numbers of this reason, it is also called the Blue Planet. There
small lumps of ice and dust (mostly ice). The is an atmospheric shield around the earth.
pieces in the rings may be as small as a milli- Besides being rich in oxygen which living things
metre or as large as a few metres across. Saturn need to breathe in order to stay alive, it prevents
is the second largest planet in the Solar System harmful ultraviolet radiation from the Sun from
and is another one of the ‘gas giants’ like Jupiter. reaching the Earth.
It takes 29.5 years to travel around the Sun. The Earth is spherical in shape, slightly flattened
Uranus : Uranus is another of the ‘gas giants’. at the poles. It bulges at the equator. An ellipsoid
You could fit 63 planets the size of the Earth flattened at the poles is described as a Geoid.
inside Uranus. Uranus takes 84 years to orbit the The Earth’s circumference is about 40,000 km.
Sun and is the coldest planet, with an average Its diameter is 12,756 km across the equator in
temperature of (–220°C). the centre and 12,713.8 km across the poles. Its
surface area is 510 million square kilometres.
Neptune : Neptune is the farthest planet from
Though this size is great, it is not vast in compari-
the Sun. It is 30 times as far as from the Sun as
son to planets such as Jupiter and Saturn.
the Earth and takes 165 years to travel around
the Sun. Neptune is the last of the four ‘gas Satellites
giants’ and is 58 times the volume of the Earth. The word ‘satellite’ means ‘an attendant’ to
A planet must orbit the sun, be large enough so anything. A satellite is a celestial body that
that its own gravity molds it into a spherical revolves round the planets. The satellites are also
shape and it must have an orbit free of other called moons. Scientists have discovered 134
small objects. such moons in the solar system up April 2005.
They are distributed as follows :
EARTH—A UNIQUE PLANET
Mercury 0, Saturn – 31, Jupiter - 60, Uranus –
The Earth is the third planet in terms of its
27, Neptune – 13, Mars – 2, Earth – 1.
distance from the Sun. This position is ideal,
because the Earth is neither too hot nor too cold. Satellites are generally smaller bodies than the
It is described as a unique planet because it is the Planets. Jupiter’s satellite Ganymede, however, is
only planet of the solar system known to support the largest satellite. It is larger than Mercury. Like
planets, satellites also shine by reflecting the light
of the Sun.

The Moon
The Moon is our nearest neighbor in the solar
system. It is the only satellite of the Earth. The
Moon is 384,400 km from the Earth. Since it is
so near from us, hence it appears so big; com-
pared to any other celestial body. The diameter
of the Moon is just one-fourth the diameter of the
Earth.
Life on the Earth
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