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|A comet's tail can be millions of kilometers in length, but the amount of matter it contains can be held in a large bookbag.|
A comet does not give off any light of its own. What seems to be light from the comet is actually a reflection of our Sun's light. Sunlight bounces off the comet's ice particles in the same way light is reflected by a mirror.
A few comets come close enough to the Earth for us to see them with our eyes. Halley's Comet, for example, can be seen from Earth every 76 years.
Since comets have no light of their own, how are we able to see them?
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