It would depend upon which series you looked at and which time they were in.
So far, I've seen almost all 50 mentioned so I would assume that that is the best answer.
There are over 100 billion galaxies (with 100 billion+ stars (each containing 9 planets and 170+ moons)) in each one; as well as asteroids and nebulae) in the Star Trek universe. Their light has taken 13 billion years to reach Earth.
Star Trek: The Original Series Star Trek: The Animated Series Star Trek: The Next Generation Star Trek: Deep Space Nine Star Trek: Voyager Star Trek: Enterprise Star Trek: Bridge Commander (TV Series)
7 Star Trek The Original Series Star Trek The Animated Series Star Trek The Next Generation Star Trek Deep Space Nine Star Trek Voyager Star Trek Enterprise Star Trek Bridge Commander (TV Series)
Star Trek spawned a generation of keen scientific minds to take some of the fictional inventions of Star Trek for example the Automatic Door and make it reality. Most people when asked would probably want an answer to the question are we alone in the Universe, and Star Trek gives us hope and perhaps inspiration for the next generation to come up with methods of uniting man kind in a common goal of bettering themsleves and exploring the universe.
Challenger - Star Trek - has 396 pages.
The Physics of Star Trek has 208 pages.
Star Trek Concordance has 256 pages.
Belle Terre - Star Trek - has 237 pages.
Shockwave - Star Trek novel - has 305 pages.
Harbinger - Star Trek novel - has 400 pages.
Abyss - Star Trek novel - has 292 pages.
Sarek - Star Trek novel - has 448 pages.