¹     It is time for another trip aboard our imaginary spacecraft. This time we are going to look for comets. It should not be too hard to find one. Scientists believe there are about 100 million comets traveling around the sun.
 
²     When people first saw comets, they did not know what to think. Some of them were afraid of the comets. The comets were "long-haired" stars to some people. They looked like flaming swords to others.
 
³     Now we know more about comets. Comets are like snowballs made of frozen gases, rock, and dust. A cloud called a coma surrounds a frozen nucleus. The coma and the nucleus together form the comet's head. They are different sizes. Most of them are about the size of a small town.

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