Photometric parallax is a means to infer the distances of
star
A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...
s using their colours and apparent brightnesses. It was used by the
Sloan Digital Sky Survey to discover the
Virgo super star cluster.
Assuming that a star is on the main sequence, the star's
absolute magnitude
Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it we ...
can be determined based on its color. Once the absolute and
apparent magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...
s are known, the distance to the star can be determined by using the
distance modulus The distance modulus is a way of expressing distances that is often used in astronomy. It describes distances on a logarithmic scale based on the astronomical magnitude system.
Definition
The distance modulus \mu=m-M is the difference between th ...
. It does not actually employ any measurements of
parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby object ...
and can be considered a misnomer.
Unlike the
stellar parallax
Stellar parallax is the apparent shift of position of any nearby star (or other object) against the background of distant objects, and a basis for determining (through trigonometry) the distance of the object. Created by the different orbital po ...
method, the photometric parallax method can be used to estimate the distances of stars over 10 kpc away, at the expense of much more limited accuracy for individual measurements.
See also
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Parallax in astronomy
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Spectroscopic parallax Spectroscopic parallax or main sequence fitting is an astronomical method for measuring the distances to stars.
Despite its name, it does not rely on the geometric parallax effect. The spectroscopic parallax technique can be applied to any main se ...
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Dynamical parallax
In astronomy, the distance to a visual binary star may be estimated from the masses of its two components, the size of their orbit, and the period of their orbit about one another. A dynamical parallax is an (annual) parallax which is computed fr ...
References
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Astrometry
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