November 24, 2012 1:37 pm

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Telescopes help us see things that are far away. They make distant objects look bigger. Using telescopes, astronomers have discovered thousands of stars, planets, moons, and many other extraordinary objects, such as black holes.
The most common type of telescope is the optical telescope. This kind of telescope gathers light from distant objects.
Imagine having eyes as big as your fist. You’d look funny, but more light would enter your eyes. You would be able to see better. Telescopes bring extra light to our eyes. They effectively make our eyes bigger. Distant objects appear larger when you look through a telescope, and you can see more detail.
A refracting telescope is the simplest type of optical telescope. It is made up of two lenses. These lenses are similar to the lens in a magnifying glass. A reflecting telescope has a lens and a dish-shaped mirror. The mirror collects and focuses (concentrates) light.
A telescope’s eyepiece can be replaced by a camera. Then the image from the telescope is recorded on film or as a digital image.
The bigger a telescope’s main lens or mirror, the more light the telescope gathers. The more light the telescope gathers, the more detail it shows, and the more distant the objects that you can see through it.
Astronomers use huge telescopes housed inside buildings called observatories. These telescopes have mirrors as large as 26 feet (8 meters) across. They gather enormous amounts of light.
Gigantic telescope mirrors are hard to build because they bend under their own weight. When a mirror bends, it makes a blurry image. One way to keep a giant mirror from bending is to divide the mirror into smaller sections. Another way to avoid huge mirrors is to use computers to combine images from several telescopes. The Very Large Telescope in Chile, for example, has four telescopes with 26-foot (8-meter) mirrors. Together they gather the same amount of light as a telescope with a 52-foot (16-meter) mirror.
Air causes another problem for telescopes. The air low in Earth’s atmosphere swirls about. This movement bends the light coming down from space just a bit, making the images we see through telescopes appear slightly blurry. To reduce this effect, large telescopes are often built on high mountains. This puts them above much of the air in the atmosphere. Many modern telescopes also have flexible mirrors. The shape of their mirrors can be automatically adjusted hundreds of times a second to adjust for the swirling atmosphere and keep the image sharp.
Optical telescopes are only one type of telescope. Astronomers also use telescopes that detect other kinds of electric and magnetic rays from space, such as X rays and radio waves. Our eyes cannot see these rays. Some objects in space aren’t bright enough to be seen with visible light. We wouldn’t know they exist without telescopes that can detect other types of radiation.
A radio telescope, for example, detects radio waves given off by planets, stars, and other objects in space. It has a huge dish that collects the radio waves and focuses them on to an antenna in the center of the dish. The dish can be turned to point at any part of the sky. The antenna turns the radio waves into electrical signals that astronomers record and study.
Several space telescopes are in orbit around Earth, beyond the atmosphere. From there, they have a perfectly clear view into space. This means they can see much more detail on distant objects.
Some types of radiation, such as ultraviolet light, X rays, and gamma rays cannot pass through Earth’s atmosphere. Telescopes that detect these types of radiation must be launched into space.
We do not know exactly who invented the telescope, but we do know it was invented in Holland at the beginning of the 17th century. The first person to look into space through a telescope was the Italian scientist Galileo. He was the first to see moons orbiting Jupiter, Saturn’s rings, and mountains on the Moon.
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