ďWhere are the rest of the planets you talked about? I canít see any of them. I can see the Moon, and earlier I saw the Sun. So whereís the other planets?Ē
ďWell, Io, you canít see them because they are millions of miles away. You can see the sun because it is gigantic. It could fit all the planets inside of it many times. The Moon isnít very large. In fact, it is smaller than most of the planets, but we can see it because it is so close to us compared to the other planets and the stars. From Earth, planets look much like the distant stars because they reflect our Sunís light.Early astronomers used lenses to make the planets seem closer. These lenses were put into tubes and called telescopes.
Before telescopes were invented, it was difficult to see distant objects in the night sky. Therefore, astronomers were limited in their progress. After the discovery of the telescope about 300 years ago, star gazing became easier, and we have found out much more about our solar system, the Milky Way galaxy, and our universe.
The earliest telescopes were the refracting and reflecting telescopes. In the 1930ís came radio telescopes that didnít need light to "see". Today we have space telescopes, which are satellite telescopes located above the Earthís atmosphere."
When the Hubble Space Telescope was brought into space by the space shuttle Discovery, it was supposed to get clearer pictures and collect better information about things in space. The Hubble did all that and much more. Using the Hubble, people have been able to find out many things about space. The Hubble has expanded our understanding of star birth, star death, and galaxy evolution. It has moved black holes from a theory to a fact. It has even downloaded over 100,000 pictures of the universe in the last eight years.
Radio telescopes were first invented in the late 1930ís. An American engineer named Grote Reber built the first one. Radio telescopes can produce images of objects in space without requiring light to "see". Radio telescopes use a bowl shaped reflector called a dish to collect radio waves in space. The reflector focuses the waves onto an antenna that changes them into electrical signals. A radio receiver amplifies these signals and records their strength. The information is analyzed by the computer to draw a picture of the source of the radio waves.
Galileo Galilee made the first refracting telescope that was used for looking at space in 1609. Using it, he discovered 4 of Jupiterís moons. He also used the refracting telescope to map the surface of the moon. James Gregory invented the reflecting telescope in 1663. He came up with the design for the telescope, but Isaac Newton actually made the first one in 1688.
We've found some great videos that show how different kinds of telescopes work. You will need shockwave on your computer to play them. Just click on the telescope, and you will open up a new window to see the video. When you're finished, just close the window and you come right back here!
Unless otherwise noted, all images courtesy of NASA. Permission for use at http://www.nasa.gov/gallery/photo/guideline.html.
This site works best on a PC using Internet Explorer. There are some minor problems using Netscape, especially on Apples, but they can't be fixed. Sorry!