Limitations

The HST cannot observe the sun because the intense light and heat would fry its sensitive instruments. Therefore, the HST is always pointed away from the sun. In addition, the HST cannot observe Mercury or Venus because they are too close to the sun. Certain stars cannot be observed with the HST because they are too bright for some of the instruments. The magnitude limitations vary with the instrument (WFPC2, NICMOS, STIS, FOC, FGS) being used.

Photo courtesy NASA The Eskimo Nebula.

In addition to the brightness of objects, the orbit of the HST also limits what can be seen. Sometimes, targets are obstructed by the Earth itself during the orbit. This can limit the time spent observing a given object. Also, the HST passes through a section of the Van Allen Radiation Belts, where charged particles from the solar winds are trapped by the Earth's magnetic field. These encounters cause high background radiation, which interferes with the detectors of the scientific instruments. No observations can be done during these periods.

Despite its flawed early history, the HST has performed well, yielding much scientific data and beautiful images. However, the HST will not last forever. Plans are underway for a new space telescope, called the Next Generation Space Telescope (NGST). NGST will be even more sensitive than HST and provide better images of even more distant objects. (See NASA's NGST page for more information.) The age of optical space telescopes started by HST promises to revolutionize astronomy as much or more than Galileo's first use of the telescope did long ago.

To see pictures captured by the Hubble telescope, check out the next page.