Halley's comet appeared once in 76 years. The period of revolution of Halley's Comet is 76 years. Halley's comet itself does not emit light, but reflects sunlight. The light of the comet is very dim, and its appearance can only be observed by astronomers with astronomical instruments. Only a few comets are seen by us. They are very bright by the sun and have long tails. When Halley's Comet appeared, it was big and bright and easy to see. It is the only short-period comet that can be seen directly from the earth with naked eyes, and it is also the only two comets that can be seen with naked eyes in a person's life. Other comets that can be seen with the naked eye will be more spectacular and beautiful, but those comets will only appear once every few thousand years.