Cool Cosmos

Background and Technology

Infrared Astronomy Takes Off

In addition to absorbing most of the infrared radiation from cosmic sources, the Earth's atmosphere itself radiates in the infrared which interferes with infrared observations. This is why it is best to get above as much of the atmosphere as possible to observe in the infrared. To do this, infrared detectors have been placed on balloons, rockets and airplanes, allowing astronomers to study longer infrared wavelengths. Even though these methods can only observe a small part of the sky for short periods of time, they have contributed much to infrared astronomy.

The first cooled telescopes were those placed on rockets which could observe the sky for several minutes before reentry. The first infrared all-sky map resulted from a series of rocket flights by the Air Force Cambridge Research Laboratory. The Air Force Sky Survey covered nearly 90% of the sky scanning at wavelengths of 4.2, 11, 20 and 27.4 microns. Although the total observation time accumulated by these flights was only about 30 minutes, they successfully detected 2363 reliable infrared sources which were published in the AFCRL Infrared Sky Survey. About 70% of these sources matched sources found by the Mount Wilson 2.2 micron survey. Rockets also found bright infrared emission from HII regions (regions of ionized hydrogen) and the center of our galaxy.

Helium filled, mylar balloons have carried infrared telescopes up to altitudes as high as 25 miles. In 1963, a germanium bolometer was attached to a balloon to make infrared observations of Mars. Beginning in 1966, the Goddard Institute of Space Sciences used balloons to survey the sky at 100 microns. Their program led to the discovery of about 120 bright infrared sources near the plane of our galaxy.

Infrared telescopes onboard aircraft such as the Kuiper Airborne Observatory were used to discover the rings of Uranus in 1977. The KAO has been used to gather infrared astronomical data for over 20 years and can fly at an altitude of 41,000 feet which is above 99 percent of the Earth's water vapor. In addition to being able to study additional infrared wavelengths, airborne observatories can detect fainter infrared objects which cannot be observed well from the ground (such as interstellar clouds).

The Kuiper Airborne Observatory

Plans are being made by NASA for a new airborne observatory. SOFIA - The Stratospheric Observatory For Infrared Astronomy will be an optical/infrared/sub-millimeter telescope mounted in a Boeing 747 and is expected to be fully operational by the year 2004.