The English astronomer Edmund Halley (1656–1742), an acquaintance of Isaac Newton’s (1642–1727), was one of the great astronomers of his time. Over his lifetime, Halley created a remarkable legacy of astronomical achievements, even developing the first weather map and one of the first scientific calculations of the age of Earth. Halley served as England’s Astronomer Royal, the highest scientific honor in the kingdom at the time, from 1719 to 1742.

One of Halley’s greatest discoveries came when he calculated the paths traveled by twenty-four comets recorded by astronomers over the years. Among these, he found that three—one visible in 1531, one in 1607, and one that Halley himself had observed in 1682—had nearly identical flight paths across the sky. This discovery led him to the conclusion that comets follow in an orbit around the sun, and thus can reappear periodically. In 1695 Halley wrote in a letter to Isaac Newton, “I am more and more confirmed that we have seen that comet now three times, since the year 1531.” Halley predicted that this same comet would return seventy-six years after its last sighting, in the year 1758.

Regrettably, Halley died before he could see that he was, indeed, correct. The comet was named in his honor, and to this day Halley’s comet remains the best-known comet in the world. It last passed by Earth in 1986, and will return again in 2062.