When you look up at the sky at on a clear night, you can see many things. The moon may be shining. If you are lucky, you may see a meteor flash across the sky. Stars are scattered all across the sky. Among the stars, you may be able to pick out some of the other planets of our solar system. Some planets, like Venus, Jupiter, and sometimes Mars, can shine brighter than the brightest stars in the sky. The furthest planets (Uranus, Neptune, and Pluto) shine so dimly, you need binoculars or even a large telescope to see them at all. But even the biggest, brightest planets just look like a tiny, bright, speck of light when you look up at them with just your eyes. Are they really tiny, or do the planets just look that way because they are millions of miles away? When you look at the planets through a powerful telescope, you discover that they are more than just tiny specks. They are entire worlds. In some ways they are like our own world, the Earth. In other ways they are very different. As we gaze up at the planets, we can't help but wonder, "How big are these other worlds?" Next Page | Intro | Diameter | Volume | Mass | | Surface Gravity | And Beyond... | NASA Ames Educator Resource Center Content and Web Development: Brian H. Day Responsible NASA Official: Donald James