TELESCOPES IN SPACE

Earth’s atmosphere is a real problem for astronomers. First, there are the clouds, of course.Then, air all by itself absorbs some of the light from outer space. The higher up you go, the more the air and the clouds are below you and the better you can see the sky above. Add in the effects of pollution and glare from city lights, and you can understand why big, new observatories are built on high mountains, far from big cities or factories, where the air is thin and dry. Even better would be to
have telescopes in space. The Hubble Space Telescope (HST) was not the first, but it’s the most
famous. It has a 95-inch (240 cm) mirror, so it’s much bigger than a backyard telescope. Being above
the atmosphere is what makes the HST so special. But there are dozens of observatories on mountaintops that have biggertelescopes than HST. It was named after Edwin Hubble, the astronomer who first measured the expansion of the universe.

Surprising Discoveries

William Herschel was looking through a reflector on March 13, 1781, when he saw a small blue dot that surprised him. Although it was just on the verge of being bright enough to see without a telescope, no one had ever recorded it before—it was the planet Uranus. Herschel’s discovery made him famous and caused a sensation in astronomy. There were new worlds in the universe to be found!

In the nineteenth century, William Parsons, Third Earl of Rosse, better known as Lord Rosse, built the biggest reflector in the world in Ireland. It was built between two large brick walls and supported by slings of rope. Lord Rosse aimed his telescope at many small, cloudy patches in the sky that astronomers had previously called nebulas. Smaller telescopes were not able to see the details in a nebula as well as Lord Rosse’s telescope.
There was a lot of debate about the true nature of these faraway objects. But in Lord Rosse’s telescope, some of them clearly showed a spiral appearance like the famous nebula in the constel- lation Andromeda. Eventually astronomers agreed that the spiral nebulas were huge galaxies similar to the Milky Way that we live 

in, and that they were much farther away than the stars that we can see with our unaided eye.
More exciting discoveries about the Milky Way and other galaxies followed in the twentieth century. Harlow Shapley found that the Solar System is in one of the spiral arms of the Milky Way, not near the center. Edwin Powell Hubble measured the motion of galaxies outside the Milky Way and shocked astronomers, in 1929, with the news that all the galaxies in the universe are rushing away from each other. This means that the entire universe is expanding. Recently, light from even more distant galaxies showed that the age of the universe is about 13,700,000,000 years old. The universe began in an awesome explosion called the big bang, and the echoes of that explosion have been observed.