Atmospheric Extinction
Atmospheric extinction varies with location and altitude. Astronomical observatories generally are able to characterise the local extinction curve very accurately, to allow observations to be corrected for the effect. Nevertheless, the atmosphere is completely opaque to many wavelengths requiring the use of satellites to make observations.
Atmospheric extinction has three main components: Rayleigh scattering by air molecules, scattering by aerosols, and molecular absorption. Molecular absorption is often referred to as 'telluric absorption', as it is caused by the Earth ("telluric" is a synonym of "terrestrial"). The most important sources of telluric absorption are molecular oxygen and ozone, which absorb strongly in the near-ultraviolet, and water, which absorbs strongly in the infrared.
The amount of atmospheric extinction depends on the altitude of an object, being lowest at the zenith and at a maximum near the horizon. It is calculated by multiplying the standard atmospheric extinction curve by the mean airmass calculated over the duration of the observation.
Read more about this topic: Extinction (astronomy)
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