Complex sentence: He has been a member of the Catalina Sky Survey in Tucson, Arizona since September, 2005 and has discovered hundreds of Near Earth and Main Belt Asteroids and three comets.
Split into simpler sentences: He has been a member of the Catalina Sky Survey in Tucson, Arizona since September, 2005. Since that time he has discovered hundreds of Near Earth and main belt asteroids along with three comets.