* Many comets are too faint to be seen with the naked eye. Even with powerful telescopes, we only detect a small fraction of the comets that exist.
* Comets come and go. They have elliptical orbits that can take them far from the Sun for long periods, making them invisible.
* New comets are constantly being discovered. Astronomers are finding new comets all the time, both with ground-based telescopes and space telescopes like NEOWISE.
So, how many comets are there?
We estimate that billions of comets exist in the outer solar system, primarily in the Oort Cloud and the Kuiper Belt.
How many comets are visible?
* A few bright comets are visible to the naked eye each year.
* More can be seen with binoculars or telescopes.
* Many are too faint to be seen even with powerful telescopes.
Instead of focusing on a specific number, it's more important to think about the vastness of the comet population and the continuous discovery of new ones.
