On this day in 240 BC, astronomers in ancient China recorded the earliest known perihelion of Halley’s Comet. The comet, whose elongated elliptical orbit takes roughly 76 years to make a full circuit around the sun, was the first comet to be understood as a cyclical or repeat visitor. Astronomer Edmond Halley discovered similarities between reports of bright comets in 1531, 1607, and 1682, which he interpreted to mean this was the same astronomical body, allowing him to correctly predict the comet would return in 1758. For this feat, Halley’s Comet was named in his honor.
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