Telluric contamination

Telluric contamination is the alteration of astronomical observations by absorption or emission from Earth’s atmosphere. It is especially consequential in spectroscopy, where atmospheric features can overlap or mimic features from celestial objects.

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Telluric absorption: The removal of selected wavelengths from light as it passes through a gas. Molecules in Earth’s atmosphere absorb starlight at characteristic wavelengths before it reaches a telescope.
Telluric correction: The removal or mitigation of atmospheric absorption and emission in astronomical data. It is the principal data-processing response to telluric contamination.
Oxygen A-band: A strong band of molecular oxygen absorption near 760 nanometers in Earth’s atmosphere. It is a conspicuous optical feature that can obscure or distort nearby astronomical spectral lines.
Interstellar absorption line: A spectral absorption feature caused by gas between a star and an observer. Interstellar lines can resemble telluric lines but remain tied to the source’s sightline and velocity.
Telluric emission: Light emitted by atoms and molecules in Earth’s atmosphere. Atmospheric emission adds spectral features to observations, especially in the near-infrared.
A0V star: A main-sequence star of spectral type A0, often used as a near-infrared calibration source. Its relatively simple spectrum makes it useful for estimating atmospheric absorption in nearby observations.
Water vapor band: A wavelength region with strong absorption by water vapor molecules. Variable atmospheric water vapor creates prominent, time-sensitive gaps in near-infrared spectra.
Instrumental response: The wavelength-dependent effect of a telescope and detector on recorded radiation. Instrumental structure can mimic atmospheric spectral distortions but originates in the observing equipment.
Atmospheric transmission: The fraction of incoming radiation that passes through an atmosphere at each wavelength. Its wavelength-dependent profile shows which parts of an astronomical spectrum the atmosphere transmits.
Molecfit: A software tool that models and corrects telluric absorption in astronomical spectra. It fits atmospheric transmission directly to observed spectra rather than relying only on a standard star.