Space Telescopes
Telescopes on Earth all have one significant limitation: the electromagnetic radiation they
gather must pass through Earth’s atmosphere. The atmosphere blocks some radiation in
the infrared part of the spectrum and almost all radiation in the ultraviolet and higher
frequency ranges. Furthermore, motion in the atmosphere distorts light. You see evidence
of this distortion when you see stars twinkling in the night sky. To minimize these problems,
many observatories are built on high mountains, where there is less atmosphere above the
telescope. Space telescopesavoid such problems completely because they are outside
Earth’s atmosphere altogether—in space.
The Hubble Space Telescope (HST), shown inFigure23.11, is perhaps the best known space
telescope. The Hubble was put into orbit by the Space Shuttle Atlantis in 1990. Once it was
in orbit, scientists discovered that there was a flaw in the shape of the mirror. A servicing
mission to the Hubble by the Space Shuttle Endeavor in 1994 corrected the problem. Since
that time, the Hubble has provided huge amounts of data that have helped to answer many
of the biggest questions in astronomy.
Figure 23.11: The Hubble Space Telescope orbits Earth at an altitude of 589 km (366 mi).
It collects data in visible, infrared, and ultraviolet wavelengths. ( 12 )
In addition to the Hubble, the National Aeronautics and Space Administration (NASA) has
placed three other major space telescopes in orbit: the Compton Gamma-Ray Observatory
(CGRO), the Chandra X-Ray Observatory (CXO) , and the Spitzer Space Telescope (SST).
Together, these four telescopes comprise what NASA calls the ’Great Observatories’.Figure
23.12shows how each of these telescopes specializes in a different part of the electromagnetic