|Summary of the Sun and Planets|
The following table lists statistical information for the Sun and the planets:
( AU )
(grs / cm 3 )
Our solar system consists of a median star that we call the Sun and the planets Mercury , Venus , Earth , Mars , Jupiter , Saturn , Uranus , Neptune , and Pluto . It includes: the satellites of the planets, numerous comets , asteroids , and meteoroids; and the interplanetary medium. The Sun is the richest source of electromagnetic energy (mainly in the form of light and heat) in the solar system. The closest known stellar neighbor to the Sun is a red dwarf star called Proxima Centauri, and is at a distance of 4.3light years . The entire solar system, along with local stars visible on a clear night, orbits the center of our home galaxy, which is a spiral disk of 200 billion stars that we call the Milky Way . The Milky Way has two small galaxies orbiting closely, both of which are visible from the southeastern hemisphere. These are called the Greater Magellanic Cloud and the Lesser Magellanic Cloud. The closest large galaxy is the Andromeda Galaxy . It is a spiral galaxy like the Milky Way but is 4 times as dense and is 2 million light years away. Our galaxy, one of billions of known galaxies, is traveling through intergalactic space.
Planets, many of the planets’ satellites, and asteroids revolve around the Sun in the same direction, in nearly circular orbits. When viewed from the top of the Sun’s north pole, the planets orbit in a counterclockwise direction. The planets orbit the Sun in or near the same plane, called the ecliptic . Pluto is a special case since its orbit is the steepest (18 degrees) and the most elliptical of all the planets. For this reason, because of its orbit, Pluto is closer to the Sun than Neptune . The axis of rotation of many of the planets is almost perpendicular to the ecliptic. The exceptions are Uranus and Pluto , which are tilted sideways.