The solar system consists of an average star we call the sun, the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. It includes the satellites of the planets, numerous comets, asteroids, meteoroids, and the interplanetary medium, which permeates interplanetary space . The sun is the richest source of electromagnetic energy in the solar system. The sun's nearest known stellar neighbor is a red dwarf star called Proxima Centauri , at a distance of about 4.3 light years. In Cosmic Perspective Our whole solar system, together with all the local stars you can see on a clear dark night, orbits the center of our home galaxy, a spiral disk of some 200 billion stars we call the Milky Way.
Interstellar space is the term given to the space between stars in the galaxy.
We are beginning to find that many stars besides the sun harbor their own planets, called extrasolar planets . As of January 2001 astronomers have detected about 50 planets orbiting other stars. They are all giant, Jupiter-like planets, made mostly of gas, since current detection methods cannot reveal smaller worlds. Their formation process is still unclear. The Milky Way has two small galaxies orbiting it nearby, which are visible from the southern hemisphere.