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Infrared Astronomy is the detection and study of the
infrared radiation (heat energy) emitted from objects in the Universe. Every
object that has a non-zero temperature radiates in the infrared. Thus, Infrared
Astronomy involves the study of just about everything in the Universe. In the
field of astronomy, the infrared region lies within the range of sensitivity of
infrared detectors which is between about 1 and 300 microns (a micron is one
millionth of a meter). The human eye detects only 1% of light at 0.69 microns,
and 0.01% at 0.75 microns, and so effectively cannot see wavelengths longer than
about 0.75 microns unless the light source is extremely bright.
Viewing the Invisible
The Universe sends us a tremendous amount of
information in the form of electromagnetic radiation (or light). Much of this
information is in the infrared, which we cannot see with our eyes or with
visible light telescopes. Only a small amount of this infrared information
reaches the Earth's surface, yet by studying this small range of infrared
wavelengths, astronomers have uncovered a wealth of new information. Only since
the early 1980's have we been able to send infrared telescopes into orbit around
the Earth, above the atmosphere which hides most of the Universe's light from
us. The new discoveries made by these infrared satellite missions has been
astounding. The first of these satellites - IRAS (Infrared Astronomical
Satellite) - detected about 350,000 infrared sources, increasing the number of
cataloged astronomical sources by about 70%.
 All Sky Map of IRAS Point Sources The plane of our galaxy runs horizontally across the image Exploring the Hidden
Universe
In space, there are many regions which are hidden from
optical telescopes because they are embedded in dense regions of gas and dust.
However, infrared radiation, having wavelengths which are much longer than
visible light, can pass through dusty regions of space without being scattered.
This means that we can study objects hidden by gas and dust in the infrared,
which we cannot see in visible light, such as the center of our galaxy and
regions of newly forming stars.
The images below, of the central region of our own
Milky Way Galaxy and of the Cygnus star-forming region, show how areas which
cannot be seen in visible light can show up very brightly in the infrared. The
top row shows these regions in visible red light. At this wavelength we are
seeing the light from billions of stars, particularly the largest, brightest
ones. Note the dark bands where vast clouds of dust block our view of more
distant objects. The middle row shows the same regions in the near infrared
(infrared wavelengths closest to visible light). Here the light we see is also
generated by stars, but now it better traces the smaller, cooler ones. Notice
how the the lanes of dust have become partially transparent, allowing us to see
things that are hidden in visible light. Our view of the central bulge of stars
in our own Milky Way galaxy is particularly striking since it is almost
completely obscured at shorter wavelengths! The bottom images show these regions
in the far infrared (infrared wavelengths farther from visible light). At these
wavelengths, stars hardly emit any light at all. Instead almost everything we
see is generated by the dust clouds themselves. The dust,
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