Objects That Radiate Infrared Light

Objects that radiate mainly at infrared wavelengths may do so because of their low temperature by astronomical standards. Objects that fall in this category start with stars of spectral classifications of K or cooler extending down the newly designated spectral classification of L. The sub-stellar classification ofBrown Dwarf links stars generating energy by nucleosynthesis to planets such as the giant and terrestrial planets in our own solar system. The planets such as the earth radiate like blackbodies at their surface 

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There are some objects that radiate predominantly by infrared light and in fact are not detectable at the shorter optical wavelengths. Historically, infrared astronomy has concentrated on these types of objects, but recently near and midinfrared observations are increasingly studying objects that traditionally have been the study of optical astronomy. 

The choice of visible or invisible colours, i.e. the range of wavelengths, in which an object or class of objects will be observed, is carefully premeditated. Pointing an infrared telescope towards an interstellar cloud, seeking out this gentle radiation, so red that it cannot be seen, the astronomer becomes sensitive to star birth, or emissions from newborn stars letting out their first cry of light from a dusty and cloudy placenta. 

When an object is heated, it emits radiation—it glows. Even at room temperature, objects radiate at infrared frequencies. Imagine a hollow sphere whose inside surface is perfectly black. That is, the surface absorbs all radiation striking it. If the sphere is at constant temperature, it must emit as much radiation as it absorbs. If a small hole were made in the wall, we would observe that the escaping radiation has a continuous spectral distribution. The object is called a blackbody, and the radiation is called blackbody radiation. Emission from real objects such as the tungsten filament of a light bulb resembles that from an ideal blackbody. 

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