Non-Optical Telescopes

In the 1980s, the era of adaptive optics began, where image analyzers were used to sense where aberrations in the image were seen. These aberrations could then be corrected in order to reduce blurring of the image. By the 1990s, giant telescopes were created using adaptive or active optic techniques. Some of these include two Keck telescopes, two Gemini telescopes, and a large binocular telescope. They involve technology that accounts for distortions in real time in order to create a very clear image.

NON-OPTICAL TELESCOPES

There are other types of telescopes that have been invented that do not use light waves in the visible spectrum. These are based on the idea that objects in the sky also give off electromagnetic radiation that is out of the range of visible light waves. Telescopes have been developed since the time of World War II that involve waves from the radio wave to gamma wave frequencies. Figure 9 shows the electromagnetic spectrum so you can see that the range of visible light is very small:

Figure 9.

Radio telescopes first became a possibility in 1931 when it was discovered that the Milky Way Galaxy emitted radio waves. This led to the first radio telescope, built in 1937. The dish was more than 30 feet in diameter; It was able to identify radio waves coming from

the sky but researchers could not identify the source of the waves. Still larger dishes were created, including the 1000-foot Arecibo telescope, built in 1963. This is shown in figure 10 as a depression that fits into the ground:

Figure 10.

There are also telescopes that use microwaves, which have a greater frequency. Some of these must be deployed into space, however, because of the fact that the signal is greatly weakened by the water vapor in the atmosphere.

Infrared radiation is usually absorbed by the atmosphere but telescopes using these wavelengths can be used high in the mountains where there isn’t much water vapor in the atmosphere. The telescopes at the top of Mauna Kea in Hawaii are this kind of telescope. An IRAS satellite telescope was launched that also looked at infrared waves for about 9 months in 1983 until its coolant ran out. Still, it was able to survey the entire sky and found about 245,000 different infrared sources.

Ultraviolet telescopes run in the high visible light frequency range. Most of this must come from satellite-based telescopes because the ozone layer will absorb a lot of this UV radiation. These must be coated with magnesium fluoride or lithium fluoride instead of silver or aluminum. One of these, the International Ultraviolet Explorer launched in 1978 was able to survey the skies for 18 years.

There are x-ray telescopes that also must be deployed on satellites to be used above the level of earth’s atmosphere. These types of telescopes were first attempted to be utilized in 1948 using sub-orbital rockets. They were able to see x-rays coming from the sun as well as from galactic sources, including the Crab Nebula. There are several x-ray telescopes of this type in play in recent years for the study of astronomical bodies.

Gamma rays are the highest frequency waves that are easily absorbed by the Earth’s atmosphere so they must be used on satellites deployed into space. These telescopes were first launched in 1967. There are certain Cerenkov radiation imaging telescopes that detect very high-energy gamma waves from the ground that exist around the world.