Synopsis The sun and the planets in the solar system such as Mercury, Venus, Earth and others are part of a galaxy. There are innumerable galaxies in the universe. The heavenly bodies move, spin on account of the gravity which each body exerts. It is mind-boggling to speculate on the size or number of the stars, planets, and the distances at which they are placed. The science of cosmology has unraveled quite a few phenomena, yet what is known is a fragment of the infinite.