World's Window - The Telescope

The Telescope

The earth receives electromagnetic radiation of all wavelengths from various directions in outer space; yet wavelengths from only two regions of the electro­magnetic spectrum are able to penetrate the earth's atmosphere freely. Most of the electromagnetic spec­trum is screened out by the atmosphere well above the earth's surface. The two spectral windows in the atmosphere through which we can observe the universe from the earth's surface are called the optical window-from about 3,000 ang­stroms to about 10,000 angstroms, or roughly the visible-wavelength region-and the radio window­which includes the wavelength region from about 1 millimeter to 30 meters. The telescopes we build on the earth's su rface to take advantage of these two windows are thus logically called optical telescopes and radio telescopes.
With the advent of the space age, astronomers have been able to take advantage of ai rcraft, balloons, rockets, and satellites to extend our vision of the uni­verse by going above part or all of the earth's veiling atmosphere. Astronomers are aghast at what space telescopes carried by these vehicles have revealed through radiation in the ultraviolet, X-ray, gamma-ray, and infrared regions.