Question

How can we distinguish between sun,star,planets,moon

Answer 1

A star is called a "sun" if it is the center of a planetary system. A large number of planets have been found that orbit other stars, thus making these stars officially "suns." Chances are that a large percentage of the stars in the galaxy also have planets orbiting them, which would make them suns as well. The number of extrasolar planets that have been detected is increasing very rapidly, as we find new planetary systems. So a large number of the stars that you see are also suns. However, many objects in the night sky are not stars. You mentioned man-made satellites, planets and the moon. From earth, there are many other objects that we see as points of light, such as far-away galaxies, so not every point of light is a star!