A moon is, astronomically, very similar to a planet, except that instead of orbiting the Sun, it orbits a planet. Our moon always presents the same side to the Earth because it rotates on its axis once during each orbit of the Earth. The lunar phases are caused by its position in space relative to the Sun and the Earth. The best time to view the moon is when it is in a crescent or gibbous phase, when shadows are longest. The stars that comprise them are usually young stars that formed out of a common cloud of interstellar gas and dust.
Open clusters are a small fraction of the age of globular clusters.
The only planets that can be readily seen from earth are the Sun's planets. Uranus and Neptune can be seen with a small telescope. The brighest quasars are the brightest objects in the universe. Click for enlargement. Site design by Mark Fairchild .