Telluric contamination is
contamination
Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc.
Types of contamination
...
of the
astronomical spectra by the
Earth's atmosphere
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing fo ...
.
Interference with astronomical observations
Most astronomical observations are conducted by measuring
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they a ...
s (
electromagnetic waves) which originate beyond the sky. The molecules in the Earth's atmosphere, however,
absorb and
emit their own light, especially in the visible and
near-IR portion of the
spectrum
A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...
, and any ground-based observation is subject to contamination from these telluric (earth-originating) sources. Water vapor and oxygen are two of the more important molecules in telluric contamination. Contamination by water vapor was particularly pronounced in the Mount Wilson solar Doppler measurements.
Many scientific telescopes have
spectrographs, which measure photons as a function of
wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...
or
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
, with typical resolution on the order of a
nanometer.
Spectroscopic
Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
observations can be used in myriad 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.
Telluric correction
It is possible to correct for the effects of telluric contamination in an astronomical
spectrum
A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...
. This is done by preparing a telluric correction
function
Function or functionality may refer to:
Computing
* Function key, a type of key on computer keyboards
* Function model, a structured representation of processes in a system
* Function object or functor or functionoid, a concept of object-oriente ...
, made by dividing a
model spectrum of a star by an observation of an astronomical
photometric standard star. This function can then be multiplied by an astronomical observation at each
wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...
point.
While this method can restore the original shape of the
spectrum
A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...
, the regions affected can be prone to high levels
noise
Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference aris ...
due to the low number of counts in that area of the spectrum.
See also
*
Pollution
Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...
and
light pollution
Light pollution is the presence of unwanted, inappropriate, or excessive use of artificial Visible spectrum, lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting, during the day ...
*
Interferometry and
astronomy
Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, g ...
*
Spectroscopy and
spectrograph
References
{{reflist
Further reading
* Christopher S. Carter, Herschel B. Snodgrass, and Claia Bryja, "Telluric water vapor contamination of the Mount Wilson solar Doppler measurements". Solar Physics volume 139, pages 13–24 (1992).
Atmosphere of Earth
Measurement
Observational astronomy