What comet was interpreted by Romans as a sign of Caesar's deification?

The comet interpreted by Romans as a sign of Caesar’s deification was Caesar’s Comet. Also called the Great Comet of 44 BC or Sidus Iulium, it appeared suddenly during public games held in Julius Caesar’s honor, several months after his assassination in March 44 BC.

Ancient writers said the comet remained visible for seven days and was understood as Caesar’s soul ascending to the heavens. Its appearance helped support the official Roman declaration that Caesar had become divine, or Divus Iulius. The event also became powerful political symbolism for his adopted heir, Octavian, later known as Augustus.

The comet was reportedly bright enough to be seen in daylight, making it especially memorable. It should not be confused with Halley’s Comet, which is a recurring periodic comet, or with Donati’s Comet, observed in the nineteenth century. Modern scholars continue to debate the comet’s exact orbit because the surviving observations are limited, but its political and religious importance in Roman culture is well established.