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Ultraviolet Telescopes, International Ultraviolet Explorer, IUE, diffraction grating, nebulas

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Telescope, device that permits distant and faint objects to be viewed as if they were much brighter and closer to the observer. Telescopes are typically used to observe the skies.

For hundreds of years, telescopes were the only instruments available for studying the planets and stars. Even today, space probes can reach only our closest neighbors in the heavens, and scientists continue to rely on telescopes to learn about distant stars, nebulas, and galaxies. Telescopes are the fundamental research instruments that enable astronomers to tackle scientific questions about the birth of the universe; the emergence of structure in the early universe; the formation and evolution of stars, galaxies, and planetary systems; and the conditions for the emergence of life itself.

Most telescopes work by collecting and magnifying visible light that is given off by stars or reflected from the surface of planets. Such instruments are called optical telescopes. Conventional optical telescopes use a curved lens or mirror to collect light and bring it to a focus, a point in space where all the light rays converge. A small magnifying lens, called an eyepiece, placed at the focus allows the image to be viewed. In astronomical research, cameras or other instruments placed near the focus make a precise recording of the light gathered by a telescope. The visible light collected by a telescope is divided into component wavelengths, or colors, through a process called spectroscopy. This powerful technique, which uses a prism or diffraction grating, essentially “decodes” starlight to yield information about an object’s temperature, motion and other dynamics, chemical composition, and the presence of magnetic fields.

Light rays, however, are just one part of what scientists call the electromagnetic spectrum. Just as stars emit visible light, they also give off other types of electromagnetic radiation, including radio waves, microwaves, infrared light, ultraviolet light, X rays, and gamma rays. All these forms of electromagnetic radiation are emitted as waves.

Rapid advances in astrophysics and optical technology, coupled with the advent of the space age, broadened telescope technology in the last quarter of the 20th century. Astronomical telescopes today come in a wide variety of shapes and sizes, dictated largely by the portion of the electromagnetic spectrum the telescope is designed to view. Telescopes today view the entire spectrum of electromagnetic radiation sweeping the universe. Each new advance in wavelength coverage has dramatically altered our view of the universe.

Many telescopes are Earth-based, located in astronomical observatories around the world. But only radio waves, visible light, and some infrared radiation can penetrate Earth’s atmosphere and reach the surface of our planet. To overcome this problem, scientists have launched telescopes into space, where the instruments can collect waves from the other regions of the electromagnetic spectrum.

Ultraviolet Telescopes

Some of the hottest and most energetic stars in the universe are visible in the ultraviolet region of the spectrum. However, this light is largely blocked by Earth’s atmosphere and so can only be studied from space. In the 1980s and 1990s a series of highly successful Earth-orbiting observatories explored the ultraviolet universe, most notably the International Ultraviolet Explorer (IUE), the Extreme Ultraviolet Explorer (EUVE), the ASTRO space shuttle observatory, and the Hubble Space Telescope (HST).

Ultraviolet telescopes are similar to optical reflecting telescopes, but their mirrors have special coatings that reflect ultraviolet light very well. Ultraviolet telescopes provide much information about interstellar gas, young stars, and the gaseous areas of active galaxies.


Villard, Ray, B.A., M.S.

Public Information Manager, Space Telescope Science Institute. Astronomy Instructor, Howard Community College.

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