Telescopes also have the advantage of being able to take a timed exposure. Our eyes don't do that. The "exposure time" of your eye would be on the order of hundreths of a second or so. Therefore, your cannot collect enough light to see dim objects.

Hubble collects light over a much larger surface. It can also take exposures that are hours or even days long. The longer the exposure, the brighter the image becomes since more light can build up (there is a limit to this process...eventually the Hubble camera will become saturated which is similar to overexposing a film picture).

Also, having a larger collecting area allows a smaller details to be seen in the image (or alternately, having two or more telescope placed a distance away from each other and doing interferometry can also increase the resolution).

And of course, Hubble is above the Earth's atmosphere as someone mentioned. It does not have to deal with the distortion which limits even the best ground based telescopes to about 1 arc second resolution on a good night (unless you use adaptive optics). You also don't have to worry about pollution, clouds, and light pollution.

The big problem is that there is only one of them and it's pretty darn expensive to make another! The NGST (Next Generation Space Telescope) has a projected launch date of late this decade and will have a larger mirror and operate in the infrared to see highly red shifted objects.

In the mean time, there is a proposal for a small infrared telescope called PRIME (Primordial Explorer) to be launched in 2005 I think. It would conduct an infrared survey of the sky, similar to the Sloan Digital Sky Survey and would be used for target selection for the NGST.

Rob

Rob