Caesar´s Comet (also Sidus Iulium ("Julian Star"); Caesaris astrum ("Star of Caesar"); Comet Caesar; the Great Comet of 44 BC; numerical designation C/−43 K1) was a seven-day cometary outburst seen in July 44 BC. It was interpreted by Romans as a sign of the deification of recently assassinated dictator, Julius Caesar (100–44 BC). It was perhaps the most famous comet of antiquity.
Based on two sketchy reports from China (May 30) and Rome (July 23), an infinite number of orbit determinations can fit the observations, but a retrograde orbit is inferred based on available notes. The comet approached Earth both inbound in mid-May and outbound in early August. It came to perihelion (closest approach to the Sun) on May 25, −43 at a solar distance of about 0.22 AU (33 million km). At perihelion the comet had a solar elongation of 11 degrees and is hypothesized to have had an apparent magnitude of around −3 as the Chinese report is not consistent with daytime visibility during May. Between June 10 and July 20 the comet would have dimmed from magnitude +1 to around magnitude +5. Around July 20, −43, the comet underwent an estimated 9 magnitude outburst in apparent magnitude and had a solar elongation of 88 degrees in the morning sky. At magnitude −4 it would have been as impressive as Venus.
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