There are many spacecraft orbiting the Earth. Some of them are "big-namers" like MIR and several space shuttles. One which briefly captivated the world was the Cosmic Background Explorer (COBE). This was the satellite which detected the small fluctuations in the microwave background radiation left over from the Big Bang. Its result was a picture which mapped the earliest density fluctuations in the universe, which were what probably gave rise to galaxy formation. However, the satellite which has expanded our horizons the most, and continues to do so, is the Hubble Space Telescope.

Hubble Space Telescope:


Courtesy of AOL's Astro Archives

The Hubble Space Telescope (HST), named after Edwin P. Hubble, was launched in 1990. However, a flaw in its primary mirror did not allow it to perform up to expectations, until a team of astronauts fixed it during a space walk in December of 1993.

Since then, the HST has returned dazzling pictures which have provided scientists with a new view of the cosmos.

The Hubble Deep Field picture was taken in 1995, and is one of the most famous pictures that Hubble has taken. It took Hubble two weeks to generate the picture, but it shows thousands of galaxies, some over ten billion years old. Pictures like this are allowing astronomers to map the visible universe.

Circling the Earth, high above the distortion effects of Earth's atmosphere, the HST has an unprecedented view of the universe. Even though its primary mirror is only 2.4 meters wide, its pictures are clearer than the twin 10 meter Keck telescopes' on top of Hawaii's Mauna Kea. This is because the curvature and turbulence of Earth's atmosphere distort views of ground-based telescopes (which is why most telescopes are built on mountain tops).

Most pictures that the HST takes are of the spectra of objects. An astrophysicist proverb states that if a picture is worth a thousand words, then a spectra is worth a thousand pictures. For example, if you take a picture of a star, then you see a point of light. But, if you take a spectra of a star, then you can see the different types of chemicals it is made of, how far away it is, and other information. Most of the 140,000 pictures that the HST has taken that have been released to the public though, are in visible light.

Other Orbiters:

Besides the HST, there are many other orbiters circling the Earth. Among them are COBE, MIR, Global Positioning Satellites, and many others. NASA had a web page called J-Track, which produces images of Earth, and shows the positions of over 500 satellites.