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There are other objects in the sky besides the clouds,
sun, and moon that we see each day.
Comets and meteoroids zoom through space,
and if you pay attention to the night sky,
you might be lucky enough to see one.
Comets, which are made from fine powdered ice, gas, and rocky dirt,
travel around our sun in much the same way the planets do.
However, a comet's orbit is longer and shaped like an oval,
so during part of its orbit,
the comet is even farther away from the sun than the outermost planets.
When a comet comes nearer to the sun,
something very interesting happens.
Energy from the sun
starts to melt off some of the icy top layer
and causes a long tail of vapor to appear from the comet.
From Earth,
a comet can look like a very bright star
with a long tail following it through the sky.
Because the energy that comes from the sun is melting the comet,
the tail always points away from the sun.
The comet will travel faster
and the tail becomes longer the closer the comet is to the sun.
The comet will slow down
and lose its tail as it travels back into the depths of space.
Comets have a very long orbit,
and take many years to complete a trip around the sun.