Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. Comet Hale-Bopp is one of the largest comets ever recorded, and although its' nucleus has never been photographed, it is estimated from brightness and spin measurements to be about 40 kilometers across. In contrast, Comet Halley in 1987 was measured to be 15 km, and Comet Hyakutake in 1996 was estimated to be no more than 10 km.
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