A day on Neptune lasts precisely 15 hours.

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A day on Neptune lasts precisely 15 hours, 57 minutes, and 59 seconds, according to the first accurate measurement of its rotational period made by planetary scientist Erich Karkoschka of the University of Arizona, Tucson. His result is one of the largest improvements in determining the rotational period of a gas planet in almost 350 years--since Italian astronomer Giovanni Cassini made the first...