QUESTION:
On what kinds of radiation does the Hubble focus?

ANSWER from Howard Lanning on April1, 1996:
HST currently has instruments onboard which can observe in three main regions
of the electromagnetic spectrum.  These include 1) the visible, from the very
blue to the very deep red wavelengths we can see with our own eyes, 2) the
ultraviolet, wavelengths just beyond the bluest visible regions, and 3) the
near infrared, regions beyond the red end of the visible and not blocked by
the earths atmosphere.  Next year, during the 2nd Servicing Mission, new
instruments will be installed which will continue to allow HST to observe from
the ultraviolet into the near infrared, but also will permit studies even
deeper into the infrared in those regions for which most of the light does not
reach the surface of the earth.

Our eyes are limited to the visible region, from 4000 to 7000 Angstroms.
Observatories on the ground can use instruments to observe a bit beyond these
wavelengths as well as radio and some small infrared bands which are not
affected by the atmosphere of the earth.  However, having a telescope in space
allows us to observe these wavelengths as well as those we can't see from the
surface of the earth.  Why observe the visible? Although we can do this from
the ground, in space, the light is not affected by the atmosphere and we can
observe in these regions in much greater detail.  Instruments like the Faint
Object Spectrograph and Goddard High Resolution Spectrograph permit us to
determine the temperature of a star or its chemical composition.  The normal
'white light' you see from the Sun is spread out like light passing through a
prism.  We can then examine individual lines of the spectrum, regions of light
absorbed or emitted by a particular element, like Hydrogen or Oxygen, for
example.  Several observers are planning observations using the spectrographs
to try and determine the makeup of the new comet Hyakutake.  Studying light in
this way also can tell us what speed an object is going, and in what direction.

Here is a list of the current and new instruments, and the wavelengths they
can be used to observe.

   WFPC2    Optical                                   1200 - 11000 Angstroms
   FOC      Optical + Ultraviolet                     1150 -  6500
   FOS      Optical + Ultraviolet + Red               1100 -  8000
   GHRS     Ultraviolet                               1150 -  3200
   STIS     Optical + Ultraviolet + Near Infrared     1150 - 10000
   NICMOS   Near Infrared                             8000 - 25000

For more information on light and the instruments used on HST, a very good
source is the new book by Peterson and Brandt, Hubble Vision:  Astronomy with
the Hubble Space Telescope.