First comet whose return was predicted, proving that at least some comets are members of the solar system .
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.