Infrared Astronomy

Infrared astronomy is providing new and fascinating discoveries and understanding about the Universe. Apart from galaxies, stars, and planets, the Universe is full of dust and gas. On a dark and clear night, you might be able to see a faintly luminous, fuzzy swath stretching across the sky - the Milky Way, as seen from the inside. Have you ever wondered why the central region of our home Galaxy, site of most of the stars, is not very bright? It is because the Milky Way, like most spiral galaxies, contains large amounts of obscuring dust within the interstellar medium.

Most stars are born in dusty environments, and hence are hidden from view. The shortest infrared wavelengths are called "near-infrared," and correspond to wavelengths of a few microns, or about 5 times longer than visible red light. The near-infrared light can pierce through the dense veil of dust and gas to reveal the underlying newborn star. The image on the left is a wide-field visible light view of a portion of the famous Orion Nebula obtained by the Hubble Space Telescope (HST). Some stars can be seen in the lower left portion of the image. However, note the dense concentrations of dust throughout the rest of the field. The region within the light blue outline, which is essentially opaque in the visible image, was also photographed by HST, but with a near-infrared camera (right image). Note how the infrared light pokes through the dust and reveals the presence of newborn stars (yellow), which otherwise would be hidden from view.
Far-infrared wavelengths (longer than 30 microns) reveal the presence of the dust. Unlike visible light, where the dust generally appears dark, the dust glows in far-infrared light. This is because the small dust particles absorb the ultraviolet light emitted by new stars, become heated, and re-radiate the energy in infrared light. These contrasting views of the familiar winter constellation Orion illustrate dramatically the difference between visible and far-infrared light.

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