* Comets are constantly being discovered: New comets are detected all the time.
* Visibility varies: Some comets are bright enough to be seen with the naked eye, while others are only visible with telescopes.
* "Seeing" a comet can be subjective: Do we mean a comet visible to the naked eye, or any comet observed by telescopes?
However, here are some examples:
* Neowise (C/2020 F3): This bright comet was visible to the naked eye in the northern hemisphere in July 2020.
* Hale-Bopp (C/1995 O1): This very bright comet was visible for months in 1997.
* Comet ATLAS (C/2020 M3): This comet disintegrated in April 2020, but was visible through telescopes for a period.
Therefore, there's no single year to answer your question. Earth is constantly being visited by comets, some more spectacular than others.
