Go to updated and illustrated post.
240 B.C. Chinese astronomers observe a new broom-shaped "star" in the sky. It's the first confirmed sighting of Halley's Comet.
Some have made the case that a sighting in 2467 B.C. is responsible for the alignment of the Sphinx and the pyramids of Giza. Interesting. Even a supposed Chinese sighting in 613 B.C. would be seven years later than the calculated 620 B.C. for a Halley's passage. Was that a record-keeping error or a different comet?
The 240 B.C. observation coincides with Halley's computed orbit, but its exact date is a matter of some imprecision. The existing Chinese record is the Records of the Grand Historian, or Shiji (or Shi Chi), written more than a century later around 100 B.C. What the Chinese called a "broom star," because of its bristly tail, appeared first in the east and then later in the north.
The text adds that it was also seen in the west during the lunar month of May 24 to June 23. Several astronomers calculated in the 1980s that the comet's closest approach to the sun was between March 22 and May 25 of 240 B.C. Those calculations also confirmed its apparent motion from east to north to west. March 30 is frequently given as the likely date for its first, though not necessarily the brightest, sighting.
Every subsequent passage of the comet was observed and recorded by astronomers in the Middle East, Asia and, eventually Europe. The 1066 appearance coincided with the Battle of Hastings, and an image of the comet was woven into the Bayeux Tapestry. Contemporary accounts say the comet looked to be four times bigger than Venus.
So, Halley: How did this guy get his name on what's probably the world's most famous comet? Edmond Halley was the British astronomer who first realized that some of history's recorded comets were in fact the same darn comet periodically returning to visibility from Earth.
Halley was using a newly discovered mathematical tool:
