Telescope

In 1609 Galileo (1564-1642), the famous Italian scientist, heard that a Dutch spectacles-maker had invented a new kind of instrument. With it he could make things faraway appear to be close.

The Dutch spectacles-maker, most accounts say, was Hans Lippershey. One story tells that a boy who was learning the trade from Lippershey was playing with some of the lenses Lippershey used for spectacles. He happened to hold one in front of another and look through them. To his surprise the lenses seemed to bring what he was looking at much closer. He showed Lippershey his discovery.

Lippershey put the two lenses in a tube. He put the new toy in his shop window. It was, of course, a simple telescope. The word telescope means "seeing far away".

As soon as he heard of a telescope, Galileo decided to make one for himself. With the first telescope he made Galileo found that he could sight vessels too far out at sea to be seen with the naked eye.

Galileo soon made better telescopes than the first one. When he finished his fourth telescope, it occurred to him to look up at the sky with it. He turned it toward the moon, and had a great surprise. The moon was not a smooth, shining ball as people had said. Instead, it had mountains and valleys and plains on it.

Ever since that time, telescopes have been used to explore the sky. There are still small telescopes for seeing distant things on the earth. But the famous telescopes have all been built to study the sky.

Galileo's telescopes were made with two small lenses. Some of the best telescopes in the world are still made with lenses. Telescopes made with lenses are called refracting telescopes.

Not long after Galileo's time the famous English scientist New­ton invented another kind of telescope. In it he used mirrors instead of lenses. Telescopes made with mirrors are called reflecting tele­scopes.

It is possible for an astronomer to study the sky by looking through the world's biggest telescopes. But scientists have found a better way of making discoveries with them. A photographic plate is a better "eye" than a real eye. Astronomers therefore use the telescopes as giant cameras. They take pictures of the part of the sky they wish to study and then study the pictures.

Дата добавления: 2015-07-20