Background and Technology
Ground Based Infrared Observations
Infrared detectors attached to ground based telescopes can detect the near-infrared wavelengths which make it through our atmosphere. The best location for ground based infrared observatories is on a high, dry mountain, above much of the water vapor which absorbs infrared. At these high altitudes, astronomers can study infrared wavelengths centered at 1.25, 1.65, 2.2, 3.5, 4.75, 10.5, 19.5 and 35 microns. Telescopes as well as our atmosphere emit infrared radiation which can complicate the observation of cosmic sources. Infrared telescopes are designed to limit the amount of this thermal emission from reaching the detectors. All ground based infrared detectors are cooled to extremely low temperatures to reduce their emission. In addition, astronomers making ground based observations measure both the emission from our atmosphere and from the object that they are observing. They then subtract the atmospheric emission from the infrared emission of a celestial object to get an accurate measurement.
By the early 1970s, it was found that the centers of most galaxies emit strongly in the infrared, including our own galaxy, the Milky Way. Quasars and other active galaxies were also found to be strong infrared emitters. All of this new information came from near-infrared observations which could be made from the ground. Today, most of the larger ground based telescopes have been modified to accommodate infrared detectors. Many ground based infrared telescopes are now using adaptive optics to create very sharp images. Adaptive optics removes the blurring of an astronomical image due to turbulence in earth's atmosphere.