Photometric parallax is a means to infer the distances of
star
A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
s using their colours and apparent brightnesses. It was used by the
Sloan Digital Sky Survey
The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project began in 2000 a ...
to discover the
Virgo super star cluster.
Assuming that a star is on the main sequence, the star's
absolute magnitude can be determined based on its color. Once the absolute and
apparent magnitude
Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...
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 sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...
and can be considered a misnomer.
Unlike the
stellar parallax
Stellar parallax is the apparent shift of position (''parallax'') of any nearby star (or other object) against the background of distant stars. By extension, it is a method for determining the distance to the star through trigonometry, the stel ...
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
The most important fundamental distance measurements in astronomy come from trigonometric parallax, as applied in the ''stellar parallax method''. As the Earth orbits the Sun, the position of a nearby star will appear to shift slightly against ...
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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 s ...
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Dynamical parallax
In astronomy, the distance to a visual binary, visual binary star may be estimated from the masses of its two components, the angular size of their orbit, and the period of their orbit about one another. A dynamical parallax is an (annual) paralla ...
References
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Astrometry
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