Page 189 - Science Class 08
P. 189
Long ago, people believed that the appearance in orbit around the earth because of the earth’s
of a comet happened by chance. However, in gravity. Satellites do not have their own light
1758. Edmund Halley, a Bri sh astronomer, like planets. They shine because they reflect
predicted the appearance of a comet. He had sunlight that falls in their surface.
observed that the path of a comet seen at The surface of the moon is covered with several
regular intervals in the path ways always the craters and mountains. It has a diameter of
same. This comet, named Halley, appears once about one-fourth that of the earth. It rotates
every 76 years. Since Halley’s me, the orbits once in its axis in the same period of me. It is
of many comets have been calculated and the about 384, 400 km away from the earth.
periods of me that they will be visible from
Why Does the Moon Change Its Shape?
the earth determined.
Moon changes its shape day-by-day because of
Halley’s comet made its last two appearances
the changes in the posi on of the earth. When
in 1910 and 1986. It is again expected to be
the moon is in between the earth and the sun,
visible around 2062.
we do not see the moon at all. It is called the
new moon (amavasya). Two or three days a er
this, we can see only a part of the moon. This is
called the crescent moon.
The largest meteorite known as Huba is 54
metric tonne. It fell on the earth’s surface in
First Quarter
1920 in South Africa.
About 10% of meteoroids reach the earth’s
surface in the form of meteorites. Waxing Waxing
Gibbous Crescent
Full Moon New
Moon Phases Moon
1. Name the other celes al bodies other
than the sun and planets.
2. What do you mean by asteroid? Waning Waning
Gibbous Crescent
3. What is ceres?
4. Differen ate between meteors and
meteorites. Last Quarter
5. Write the composi on of comets.
6. Why are meteors also called the shoo ng A er a week, we can see half of the moon. This
stars? is called the first quarter. When we see more
7. Who discovered the Halley comet? than half of the moon, it is called the gibbous
moon. Gradually, the moon becomes bigger
and bigger and on the fi eenth day, we see the
EARTH’S NATURAL SATELLITE
full moon (purnima) when the earth comes
A heavenly body that revolves around a planet
between the sun and the moon. These are
is called natural satellite. Our earth has only
known as the phases of moon.
one natural satellite called the moon. It is held
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