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Our Solar System

A Practical Guide to Astronomy

From our small world we have gazed upon the cosmic ocean for thousands of years. Ancient astronomers observed points of light that appeared to move among the stars. They called these objects planets, meaning wanderers. The words "solar system" refer to the Sun and all of the objects that travel around it. Our solar system is made up of a star – the Sun – nine planets, 138 moons and a bunch of comets, asteroids and other space rocks.

Our solar system is part of a galaxy known as the Milky Way and the Sun is the center of the solar system. Astronomers believe the solar system formed 4.5 billion years ago. The Sun contains 99.8% of all of the mass in our solar system. This mass has a tremendous gravitational pull on planets, satellites, asteroids, comets, and meteoroids. The stargazers also observed comets with sparkling tails, and meteors or shooting stars apparently falling from the sky. Asteroids and comets orbit our Sun in a flattened circle called an ellipse.