Infrared Devices
In 1800 William Herschel detected the infrared component of solar radiation by positioning thermometers beyond the red end of the sun's visible spectrum and thus foreshadowed the astronomy of invisible spectral regions. What we have seen over the last 15 years in these regions has revolutionized our concept of the universe.
INFRARED TELESCOPES
We can subdivide the infrared spectrum into three segments. A large part of the infrared spectrum is not visible at ground level because of absorption by water vapor, carbon dioxide, and molecular oxygen, which lie between the ground and about 15 kilometers altitude. Consequently, airplanes, balloons, rockets, and satellites are extensively used to lift the infrared telescope above the veiling atmosphere. Astronomers can also locate infrared facilities on mountaintops, such as the one in the Hawaiian islands to make ground-based infrared observations.
The liquid-helium-cooled infrared detector can be used with the appropriate analyzing instruments on an ordinary optical telescope to study the cosmos. But because of the longer wavelength of infrared radiation, the image-producing quality of the telescope objective need not be so fine as it must be for the visible region. Thus a number of new telescopes have been designed and built for infrared astronomy only. A national observatory for infrared astronomy is built high on the 4200-meter inactive Hawaiian volcano Mauna Kea. A 3.0-meter infrared telescope constructed by NASA and the University of Hawaii is in operation there along with a 3.B-meter infrared telescope belonging to the United Kingdom. Other major infrared telescope facilities are the MMT in Arizona, the University of Wyoming facility, and Mexico's 2.1-meter reflector.
