Halley's Comet

or Comet Halley

First comet whose return was predicted, proving that at least some comets are members of the solar system. Edmond Halley showed in 1705 that comets seen in 1531, 1607, and 1682 were really one comet, and he predicted its return in 1758. Later calculations identified it with the large, bright comet seen during the Norman Conquest (and depicted in the Bayeux Tapestry) and with other comet sightings at intervals of about 76 years, the first in 240 BC. The only easily seen comet that returns in a single lifetime, it approached Earth twice in the 20th century (1910, 1985–86). Its nucleus is roughly 9 mi (15 km) across.

Find more information on Halley's Comet. Upgrade to Britannica Online for more on Halley's Comet.