Astronomy

At its most fundamental, astronomy is based on the electromagnetic radiation emitted by the stars. The ability to gather light is the key to acquiring useful data. The bigger the primary mirror of a telescope, the greater its light-gathering capabilities and the greater the magnification of the instrument. These two attributes allow a large telescope to image fainter, smaller objects than a telescope of lesser size. Thus, astronomers build everlarger telescopes, such as the 33-ft-diameter (10-m) Keck telescopes in Hawaii, or escape the distorting effects of the atmosphere with orbital observatories like the Hubble Space Telescope.

Astronomy is not just about visible light, however. Though the visible spectral region is most familiar to us because our eyes are optimized for these wavelengths, observation in the visible region shows only a small portion of the activities and processes underway in the universe. When astronomers view the night sky in other regions of the electromagnetic spectrum, it presents an entirely different picture. Hot gases seethe and boil when viewed at infrared wavelengths, newly forming galaxies and stars glow with x rays, and mysterious objects generate explosive bursts of gamma rays. Radio wave and ultraviolet observations likewise bring astronomers new insights about stellar objects.

Each spectral region requires different instrumentation, and different approaches to data analysis. Radio astronomy, for example, is performed by 20- and 30-ft-diameter (6- and 9-m) antennas, or even telescopes like the one in Arecibo, Puerto Rico, in which a 1,000-ft (303-m) diameter natural bowl in the landscape has been lined to act as an enormous radio wave collector. In the Very Large Array in New Mexico, 27 antennas placed as much as a mile apart from one another are linked by computer to make simultaneous observations, effectively synthesizing a telescope with a 22-mi (35-km) aperture—a radio-frequency analog to the Keck telescope. Infrared, x-ray, and gamma-ray telescopes require special materials and designs for both the focusing optics and the detectors, and cannot be performed below the Earth's atmosphere.