First Heliocentric Model
Our Solar System
First Heliocentric Model



Our planet Earth is located in what is called the Solar System. This consists of a star, which we call the Sun, nine planets that orbit the sun, and a large number of moons that orbit all but two of the planets. Additionally, there are a large number of asteroids that orbit mostly between Mars and Jupiter, comets, meteroids and dust. In the 1990s an outer icy asteriod belt beyond the orbit of Neptune was discovered, known as the Kuiper belt, containing icy objects, and a hypothesized Oort cloud much further from the sun that may contain a reservoir of many of the long period comets.

By using various dating methods, the solar system has been found to be about 4.5 billion years old. With the exception of Pluto, the planets including the earth, all orbit close to the same plane, and are generally in fairly circular orbits. Consequently the solar system can approximately be represented by concentric circles on a sheet of paper like a bull's eye with the sun at the center. However, because the distances separating the planets are so large compared to the sizes of the planets and the sun, it is impossible to represent on the same diagram the distances and sizes of the planets on the same scale.

Click on the links on the left to find out more about the Sun, the planets and their moons, and the asteroids and comets.

I am employed in research at the University of Arizona in the Department of Astronomy, where I am working on planets in orbit around other stars. The first such planet was found in 1995, and about 160 (as of March 2005) are now known. I am not currently engaged in teaching at the University of Arizona, and this website is a personal site that has nothing to do with the Department of Astronomy.

If you are interested in having more information, please e-mail me at or

This site was last updated on 03/23/05.

© Arizona Board of Regents 2005

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