(Submitted November 12, 1997)
When was the earliest known sighting of a comet made?
Unfortunately, none of us here know when the earliest surviving record of a
comet observation was. Comets have existed for longer than life has been
on Earth, so the first time one was seen by a human was shortly after the
time of the first human.
Aristotle (b. 384 BC) wrote about comets in his _Meteorology_ (~350 BC).
However, this talks about comets in general, I haven't read the whole thing
to see if he discusses any specific apparitions. According to Plutarch, a
comet was seen in the sky after Julius Caesar's death in 44 BC (mentioned
in Shakespeare) and Tacitus talks of a comet in the late days of Nero
(still later). This demonstrates how a good search engine can be more
useful than erudition. I knew only of Caesar's comet before using the
Seneca wrote about comets, apparently compiling a catalog. However, the oldest specific recorded comet we have found (on the Web at
least) was the Chinese observation of Halley's comet in 240 BC
To find the oldest recorded comet sighting, you should look for the oldest
astronomical records. This can include mythology and other traditional
literature, astronomical records from China, Egypt, Mesoamerica and other
ancient cultures etc.
for Ask an Astrophysicist
Questions on this topic are no longer responded to by the "Ask an Astrophysicist" service. See http://imagine.gsfc.nasa.gov/docs/ask_astro/ask_an_astronomer.html
for help on other astronomy Q&A services.