In 1608, a Dutch eyeglass maker named Hans Lippershey looked at a church steeple through two lenses placed one in front of the other and saw that the image was magnified. Unfortunately the telescopes built on Lippershey's model had poor image quality, caused by the bending of light though the glass lenses. (Glass does not bend the different colors of light equally. Red light is bent the least causing a colour distortion in the image.) Isaac Newton eventually solved this problem in 1668 by making a telescope that worked with mirrors instead of lenses.
Galileo Galilei was the first person to use the telescope to seriously study the heavens. Galileo was able to see that the moon was not smooth, but covered with huge valleys and craters. He discovered four moons orbiting Jupiter and found out that Venus has phases just like the moon. He realized that this must mean that Venus, and the other planets, revolve around the sun not around the earth, as many people believed at the time. In 1610 Galileo published a book about what he had seen through his telescope. Starry Messenger became the seventeenth-century equivalent of a bestseller. Not bad!
How It Works
Telescopes make it possible for astronomers, and us, to study the universe. Pretend we are outside one evening with our telescope looking at a planet, say Venus. (We are definitely better off studying this poisonous, acid-cloud obscured planet through a telescope instead of in person.)
When we turn our telescope on Venus, an image of the planet is produced inside the telescope tube. Depending on the type of telescope we use, lenses or a combination of lenses and mirrors help our eyes gather more light so we see Venus better. Because most telescopes invert images, we see Venus upside-down. This doesn't really matter except when trying to find the North and South Poles. Some telescopes have another set of lenses that turn the image upright.
Refracting telescopes (or refractors) use lenses to gather and bend light making things seem larger. The lenses used in refracting telescopes are called concave and convex. Convex (curved outward) lenses make things bigger, but blurry. Concave (curved inward) lenses make things look clearer, but small. As you can guess, a combination of these two lenses makes things seem bigger and clearer.
Imagine we are still outside looking at Venus with a refracting telescope. What happens when you look through the telescope? An objective, or large, lens collects light from Venus and sends it to a smaller, eyepiece lens at the back of the telescope tube. The eyepiece magnifies the little image of Venus and directs it at your eye. Wow, can you see the yellow-white disk? Now that's some planet!
Let's say we are still outside looking at Venus, but now we are using a reflecting telescope (or reflector). Our reflecting telescope uses mirrors to collect and magnify light. Remember that reflecting telescopes originally developed to solve the problem of colour distortions caused by lenses bending light at different angles. The reflecting telescope's mirror reflects light instead of bending it so there is no colour distortion.
With our reflecting telescope, light is collected by a big concave mirror. The mirror reflects light to a smaller flat mirror. This secondary mirror directs the light from Venus through the eyepiece lens at the side of the telescope. The eyepiece magnifies the image. Yep, when we look through the eyepiece, we can see Venus. Hey, it's starting to get cold out here. Enough planet-watching for now, let's go inside and get some hot chocolate!
Telescope Facts
The largest optical telescope in the world is in Hawaii. It's the 10-meter W. M. Keck telescope. At 4300 meters, it sits on top of Mount Mauna Kea, an extinct volcano.
Radio telescopes use a large dish to collect radio waves from space. The dish is the same shape as the mirror of a reflecting telescope. Radio telescopes are a valuable tool for astronomers since many objects in the universe do not produce enough visible light to be picked up by optical telescopes. One of the world's most powerful radio telescopes is the Very Large Array (VLA) in New Mexico. The VLA is made up of 27 linked radio telescope dishes each 25 meters in diameter.
