Halley's Comet is the most famous of the short-period comets (with an orbit lasting 200 years or less) and it is also the only one of this type which is visible from Earth by naked eye. Halley's frequency is every 75 years. It was first seen about 240 BC, and its appearances have been recorded since then, but nobody found out that it was the same comet reappearing until 1705, when the English astronomer Edmond Halley discovered it (and that's where the name of the comet came from).