telluric line

A telluric line is an absorption line due to Earth atmosphere within the observation data of ground telescopes. In studying astronomical bodies, such lines constitute a distortion of the target body's spectrum (termed telluric contamination), and are a motivation for space telescopes. The contamination is not the same everywhere and all the time: it depends upon weather conditions, altitude, etc. Telluric correction and telluric line subtraction are terms for efforts to tease out the astronomical data from that contributed by Earth atmosphere. For stars, a well-established method is during observation, include within your FOV a star with known spectral energy distribution (termed a telluric star), which would reveal the telluric contamination at the time and place, allowing it to be quantified. Compensating for telluric lines is vital for very precise/accurate radial velocity measurements using HRS. Advanced methods using post-processing are now used, such as methods using principal component analysis (PCA).