Here's why:

* Our solar system alone has over 200 moons: We've discovered over 200 moons orbiting planets in our own solar system, with Jupiter and Saturn having the most.

* Exoplanets and their moons: We've discovered thousands of exoplanets (planets outside our solar system). Many of these exoplanets likely have moons as well, although we haven't directly observed them yet.

* Ongoing discoveries: Astronomers are constantly finding new moons and exoplanets. The number of moons in the universe is constantly growing.

It's impossible to know the exact number of moons, but it's safe to say there are millions, if not billions, of moons out there.