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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 (see Optics).
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 (see Electromagnetic
Radiation). 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 .
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