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Hale-Bopp comet. Photo: NASA


A small space object made of dust and gases. Comets travel around the sun in long, cucumber-shaped paths. Far out in space they are round and dark. When they come near the sun, they begin to glow and some comets grow a “tail.” The tails are made of thin gas and dust blown away from the body of the comet by the pressure of sunlight. The most famous comet is Halley’s comet, which last visited Earth in 1986. [Comet comes from a Greek word meaning “long-haired.” To the Greeks a comet seemed to have long hair flowing out behind it.]