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.
Hubble Space Telescope
The Hubble Space Telescope,
free of the distorting effects of the earth's atmosphere, has
an unprecedented view of distant galaxies. Placed in orbit in
1990, scientists discovered soon after the telescope became operational
that its 240-cm (94.5-in) primary mirror was flawed. However,
a repair mission completed by space shuttle astronauts in December
1993 successfully installed corrective optics which compensated
for the flawed mirror.
Stellar Nursery in Infrared
The Infrared Space Observatory
(ISO) detects infrared, or heat, radiation in space. It can see
through clouds of interstellar dust because infrared radiation
is not blocked by the dust as much as visible light is. The ISO
took this picture of new stars forming out of a cloud of dust
and gas. The stars are not visible to optical telescopes because
the visible light that they emit is blocked by the dust surrounding
them.
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 light, they also give off other types of electromagnetic radiation, including radio waves, microwaves, infrared light, visible 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, has broadened telescope technology in recent decades. Astronomical telescopes today come in 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 the 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.