they have long elliptical orbits
Thousands of reported sightings over hundreds of years.
Many in the past few years.
There is no set number, because new comets are discovered all the time. Not all comets that are discovered will be visible with the naked eye.
YES there have been many many many many ufo sightings in california
There have been many sightings over India, especially in the years 2008 & 2009.
There have been a lot. I don't think anyone knows how many. The question is how many were really sightings and how many were made up. That is the problem with all of this. Do I believe there are actual sightings? Yes.
There are no comets on Neptune because Neptune is a planet and comets are, well, comets. They have nothing to do with each other.
6
the next one is set to cycle on July 12, 2126
36 years
3 years
Many astronomers have discovered that many comets. For example, David Levy is the discoverer or co-discoverer of 22 comets.