Page 186 - Science Class 08

The four outer planets are of Jupiter, Saturn, The earth’s surface has mountains, canyons,
Uranus and Neptune.
The Inner Planets
Mercury : Mercury is the planet closest to the
sun. It has a diameter of 14880 km. It revolves
around the sun faster than any other planet.
One Mercury Day is equal to 88 Earth Day. One
Mercury Year is equal to 59 Earth Year. Mercury
has no moons. It has a surface similar to that of
the earth’s moon. It is a barren desert with
mountains and craters. At the equator of
Mercury, the temperature ranges from – 183 °C
during a Mercury night to 330 °C at moon on a
Mercury Day. This temperature is hot enough
to melt lead or n. Mercury is visible on the sky
only very close to the horizon for a short period
of me just before sunrise or just a er sunset.
Venus : Venus appears as a bright object in the
morning or evening sky. It is visible without a
telescope. That’s why Venus is also called a
morning or evening star. Venus has a diameter
of 12100 km. It orbits the sun at an average
distance of 108 million km. This distance places
Venus’s orbit close.
Venus rotates from east to west . On Venus, the
sun rises in the west and sets in the east. A
Venus Day is equal to 243 Earth Days and a
Venus Year is equal to 225 Earth Years.
Earth : Viewed from the space, the earth looks
like a blue sphere with white streaks. The blue
is caused by light reflec ng from the oceans
and the white is clouds.
The earth is a unique planet because it
supports life on it. The atmosphere of the earth
contains nitrogen and oxygen. Oxygen is vital to
life and nitrogen is part of every living
organism. The average temperature of the
earth is 14 °C. About 71 percent of the earth’s
surface is covered with water.
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deserts, basins and even a few craters.
The earth revolves around the sun. It makes a
complete revolu on of the sun in about 365.25
The Earth Days. The earth rotates once on its
axis every 24 hours. The diameter of the earth
is 12756 km. The earth has one natured
satellite, the moon. It also revolves around the
earth and rotates on its axis in 27.3 days each.
It is about one-fourth of the earth’s diameter,
about 90 moons can fit in the earth.
Mars : Mars is visible from the earth without a
telescope. Mars has a diameter of 6743 km.
The length of its day is 24 hours, 37 minutes
according to the earth me. Its year is equal to
687 Earth Days. Mars has two moons, Phobos
and Deimos. Phobos has a diameter of 27 km,
and Deimos has a diameter of 15 km. A year on
Mars has seasonal changes. Astronomers have
observed ice caps at the poles. These ice caps
change in size. As one ice-cap changes in size as
one ice-cap expands the other cap retreats.
No life has been detected on Mars so far. The
surface of Mars is covered with craters. Four
giant volcanoes are found on this planet. They
are all inac ve. The largest volcano, Olympics
Moons, is three mes as tall as the earth’s
Everest. It is 550 km across its base.
Temperatures on Mars range from about room
temperature, 21°C to –100°C. The thin
atmosphere is mainly carbon dioxide. Winds
near the surface can blow enough dust into the
air to make the planet’s surface invisible for
months.
Outer Planets
Jupiter : Jupiter is the largest planet. Its
diameter is 143200 km, which is eleven mes
that of the earth. Jupiter is the second biggest
planet in our solar system. Because of its great
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