Re: How many moons does Uranus have?

Uranus has AT LEAST 21 moons.  What that means is that 21 moons have been
seen so far.  There could be smaller moons that we haven't seen yet.  

Why you sometimes see that there are 15 moons is because at one time that
is how many we had seen.  Until 1997, only 15 moons had been discovered.  5
moons were discovered by people looking through telescopes, 10 more moons
were discovered by the Voyager spacecraft that flew by Uranus in 1986.  But
since 1997, 6 more moons have been discovered - that adds up to 21.  The
most recent discoveries were in 1999 - so perhaps there will be future
discoveries and we'll have to change the number again!