[JOAN CARTAN-HANSEN] The Hubble telescope is about the size of a school bus and weighs 12.5 tons. It travels at about 17,500 miles per hour and circles the earth once every 96 minutes. It's an optical telescope - that is, it gathers light with a mirror. There are 2 kinds of optical telescopes. Refracting telescopes use 2 lenses and a long tube. That's the kind Galileo used in 1609. The other is a reflecting telescope. This kind of a telescope uses a curved mirror to focus light. The Hubble is a reflecting telescope.

The Hubble was named after Edwin Hubble, one of the 20th century's greatest astronomers. He discovered that the universe is expanding - part of the big bang theory of how our universe began.

The Hubble telescope was sent into space inside the space shuttle in 1990. Astronauts placed the telescope in orbit around the earth and everything seemed to be going okay. But the first images the Hubble sent back were out of focus. It seems the mirror inside the Hubble was slightly the wrong shape - off by 1/50th of the thickness of a sheet of paper at its outer edge. In 1993 astronauts fixed the Hubble during a servicing mission and have made 5 repair trips in total. They've had to. Space is a tough place for a telescope.

The Hubble is made up of 100,000 different parts and sometimes things wear out or need to be replaced by newer, better equipment. It's dangerous work but the results are spectacular.

The Hubble uses different cameras to take pictures of different things. Some look at the large areas of the sky. Others focus on one target - say a black hole. Scientists on the Hubble project also use spectrographs to study the light coming from the stars.

Spectrographs separate light into different colors and then measures how much of each color or light there is. That way astronomers can tell how old a star is and what elements it's made up of. So what can't the Hubble see? Well, it can't see things on Earth because it's moving too fast compared to the ground and it can't study the sun because the sun is too close and too bright.

So why have a telescope in space at all? Why not just use more powerful telescopes on Earth? Well, the earth's atmosphere scatters light making images blurry. The Earth's atmosphere also blocks some colors of light. But because the Hubble is outside the Earth's atmosphere it can see objects 50 times fainter than can be seen here on the ground and its camera is the ultraviolet and the infrared light. But even that isn't good enough for some astronomers. Scientists are planning a whole new generation of space telescopes.

The James Webb space telescope will eventually orbit about a million miles from Earth opening up new vistas for astronomers to explore.

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