of the astronomical spectra
by the Earth's atmosphere
Interference with astronomical observations
Most astronomical observations are conducted by measuring photons
) which originate beyond the sky. The molecules in the earth's atmosphere, however, absorb
their own light, especially in the visible and near-IR
portion of the spectrum
, and any ground-based observation is subject to contamination from these telluric (earth-originating) sources. Water vapor, oxygen, and OH are some of the more important molecules in telluric contamination. Water contamination was particularly pronounced in the Mount Wilson solar Doppler measurements.
Many scientific telescopes have spectrographs, which measure photons as a function of wavelength or frequency, with typical resolution on the order of a nanometer. Spectroscopic observations can be used in a myriad of contexts, including measuring the chemical composition and physical properties of astronomical objects as well as measuring object velocities from the Doppler shift of spectral lines. Unless they are corrected for, telluric contamination can produce errors or reduce precision in such data.
Telluric contamination can also be important for photometric measurements.
It is possible to correct for the effects of telluric contamination in an astronomical spectrum. This is done by preparing a telluric correction function, made by dividing a model spectrum of a star by an observation of an astronomical photometric standard stars. This function can then be multiplied by an astronomical observation at each wavelength point.
While this method can restore the original shape of the spectrum, the regions affected can be prone to high levels of noise due to the low number of counts in that area of the spectrum.
- Christopher S. Carter, Herschel B. Snodgrass, and Claia Bryja, "Telluric water vapor contamination of the Mount Wilson solar Doppler measurements". September 30 1991.