In
astronomy
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...
, a photometric system is a set of well-defined
passband
A passband is the range of frequency, frequencies or wavelengths that can pass through a Filter (signal processing), filter. For example, a radio receiver contains a bandpass filter to select the frequency of the desired radio signal out of all t ...
s (or
optical filters), with a known sensitivity to incident radiation. The sensitivity usually depends on the optical system, detectors and filters used. For each photometric system a set of
primary standard stars is provided.
A commonly adopted standardized photometric system is the Johnson-Morgan or
UBV photometric system (1953). At present, there are more than 200 photometric systems.
Photometric systems are usually characterized according to the widths of their passbands:
* broadband (passbands wider than 30 nm, of which the most widely used is Johnson-Morgan UBV system)
* intermediate band (passbands between 10 and 30 nm wide)
* narrow band (passbands less than 10 nm wide)
Photometric letters
Each letter designates a section of light of the
electromagnetic spectrum
The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high ...
; these cover well the consecutive major groups, near-
ultraviolet
Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...
(NUV),
visible light (centered on the V band), near-
infrared
Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
(NIR) and part of mid-infrared (MIR). The letters are not standards, but are recognized by common agreement among
astronomers and
astrophysicists.
The use of U,B,V,R,I bands dates from the 1950s, being single-letter abbreviations.
With the advent of infrared detectors in the next decade, the J to N bands were labelled following on from near-infrared's closest-to-red band, I.
Later the H band was inserted, then Z in the 1990s and finally Y, without changing earlier definitions. Hence, H is out of alphabetical order from its neighbours, while Z,Y are reversed from the alphabetical – higher-wavelength – sub-series which dominates current photometric bands.
Note: colors are only approximate and based on wavelength to sRGB representation (when possible).
Combinations of these letters are frequently used; for example the combination JHK has been used more or less as a synonym of "near-infrared", and appears in the title of many
papers.
Filters used
The filters currently being used by other telescopes or organizations.
Units of measurements:
* Ã… =
Ångström
* nm =
nanometre
* μm =
micrometre
The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...
Note: colors are only approximate and based on wavelength to sRGB representation (when possible).
See also
*
Photometry
*
AB magnitude
References and footnotes
External links
*
Johnson, H. L.;
Morgan, W. W. (1953), ''Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas'', The Astrophysical Journal, vol. 117, pp. 313–35
The Asiago Database on Photometric Systems* Michael S. Bessell (2005), ''STANDARD PHOTOMETRIC SYSTEMS'', Annual Review of Astronomy and Astrophysics vol. 43, pp. 293–336
Infrared portrait of the nearby massive star-forming region IRAS 09002-4732 Apai, D.; Linz, H.; Henning, Th.; Stecklum, B., 2005
{{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System
Photometric systems,