Infrared Astronomy

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What is infrared astronomy?

It is simply the study of our Universe at wavelengths longer than visible light, but shorter than radio waves; that is, at wavelengths between roughly 1 micron and 1000 microns (1 millimeter).
How long has infrared astronomy existed?
Infrared astronomy is one of the newest types of astronomy, primarily because of the technologies required. Near-Infrared astronomy (that is, observations at short IR wavelengths of a few microns) has been practiced from ground-based telescopes since the 1960s. Observations at longer wavelengths are obscured by the Earth’s atmosphere. Some infrared astronomy observations were made aboard high-flying airplanes in the 1970s. The first space-borne infrared telescope, the InfraRed Astronomical Satellite (IRAS), orbited the Earth in 1983.
What kinds of astronomical objects emit infrared light?
Most astronomical phenomena emit at least some infrared light. Nevertheless, some wavelengths are better suited for studying certain objects than others. Thermal infrared radiation measures relatively cool astronomical phenomena, corresponding roughly to room temperature or lower. These phenomena include planets, comets, and dust in the interstellar medium of galaxies. Infrared light is useful for examining dusty regions that have been warmed by newborn stars, and for studying discarded shells of matter from dying stars.
What is the interstellar dust made of?
Most interstellar dust is made of silicates, the same molecular materials as sand. Some smaller interstellar dust particles are carbon-based molecules.
How does interstellar dust produce infrared light?
The silicate dust particles absorb ultraviolet and visible light emitted by nearby stars and re-radiates the light as infrared radiation. Since the IR light is of lower energy than the UV/visible light, the difference went into heating the dust grain. Typical temperatures for interstellar dust grains are tens of degrees Kelvin, or way below zero (Celsius and Fahrenheit). For more technical information about interstellar dust, please visit these Web sites:
Why is infrared astronomy important?
Many of the fundamental mysteries of astronomy are best studied in the infrared. Why? Let us count the reasons!
  1. The Hubble expansion of the Universe redshifts the optical radiation from distant objects into the infrared region of the spectrum. Hence, IR observations can probe the Universe as it was when it was only a fraction of its present age.
  2. Dust is a very effective absorber and re-radiator of optical and ultraviolet light. Therefore, much of the radiant energy in the Universe is found in the infrared.
  3. Many of the Universe's constituent parts (such as galaxies and stars) are found in dusty environments. The only way to peer into the obscured cocoons of star formation and into the heart of dusty galaxies is through infrared eyes.
  4. The Universe is a cool place! Many astrophysical phenomena are relatively cool (planets, interstellar gas and dust), and hence radiate primarily at infrared wavelengths.
  5. The infrared region is home to a very large number of the most important atomic and molecular transitions. The resulting IR spectral features are important diagnostic tools for understanding physical conditions and processes in planetary atmospheres, interstellar clouds, and in distant galaxies.
  6. As NASA's Origins Program will seek to exploit, the mid-infrared region is where the elementary spectral lines indicative of life-sustaining environments are located.
What do infrared astronomers look for?
Infrared astronomers look for a variety of objects in space. Since infrared radiation is emitted by just about every object in space we can detect most phenomena in the Universe with sensitive enough detectors. Several objects are best studied in the infrared. These include cool stars which are too faint to be detected in visible light, star forming regions which are embedded in thick dust and cannot be seen in visible light (infrared can penetrate dust), starburst glaxies, our galactic center, planets, asteroids, light from the distant Universe which has been red-shifted or Doppler shifted into the infrared, and the dust between the stars.

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