Space Telescopes

Why Space Telescopes?

A space telescope is not fundamentally different from any telescope used on the surface of the Earth. However, they have a (deserved) reputation for being more powerful, and being able to see further. Why?

When a telescope is based on the surface of the Earth, light from a distant star must first pass through the Earth's atmosphere before it reaches the telescope. Though the atmosphere seems transparent to human eyes, it causes a lot of the stars' light to be filtered out. Also, some of the light is refracted in the atmosphere, which makes the images a bit fuzzy.

For this reason, some telescopes have been built at higher altitudes, because they will have to look through a smaller amount of atmosphere. The Keck Observatory in Hawaii is one example of this.

Background light also plagues groubd-based astronomy. People produce a lot of artificial light, and much of it is scattered by the atmosphere, making it appear that the sky is glowing slightly. This makes it very hard to see any stars that are fainter than the sky. The small amount of celestial light that travels through the atmosphere is overwhelmed.

The Hubble Space Telescope

The Hubble Space Telescope was launched in April 1990. From the start, it experienced technical problems. One of the solar panels didn't deploy properly, which threw the entire telescope off balance, making it difficult to focus. Even more problematic, though, was an imperfection in the shape of one of the mirrors. This caused the images to be distorted. However, repairs were performed in 1993.

Since the Hubble Space Telescope began operating, it has provided data for more than 2500 scientific papers. It has observed more than 25,000 distinct astronomical targets It has been one of the primary observatories for astronomers around the world.

The James Webb Space Telescope

The James Webb Space Telescope is expected to launch in 2011, and is designed to continue the same program of discovery that the Hubble began. This telescope will have a primary mirror that is more than twice the size of Hubble's. It is expected to be able to observe objects four hundred times fainter than Hubble is capable of, with the same high resolution.

The James Webb Space Telescope will be different from the Hubble in another respect: rather than being placed in Earth orbit, it will be at a point more than one million miles from the Earth. This will make its observations in the infrared range of light much more accurate. Being far from Earth means, however, that the James Webb Space Telescope will not be serviceable as Hubble was. This means that it must be built to last and cannot be repaired if there are any failures.