In
astronomy
Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
, a photometric system is a set of well-defined
passbands (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
The UBV photometric system (from ''Ultraviolet, Blue, Visual''), also called the Johnson system (or Johnson-Morgan system), is a photometric system usually employed for classifying stars according to their colors.
It was the first standardized ...
(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 range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from ...
; these cover well the consecutive major groups, near-
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiati ...
(NUV),
visible light (centered on the V band), near-
infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from aroun ...
(NIR) and part of mid-infrared (MIR).
The letters are not standards, but are recognized by common agreement among
astronomers and
astrophysicists
The following is a list of astronomers, astrophysicists and other notable people who have made contributions to the field of astronomy. They may have won major prizes or awards, developed or invented widely used techniques or technologies within ...
.
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.
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
Paper is a thin, flat material produced by the compression of fibres.
Paper(s) or The Paper may also refer to:
Publishing and academia
* Newspaper, a periodical publication
* ''Paper'' (magazine), an American monthly fashion and culture magazin ...
.
[ Example of use of J for "near-infrared"]
Filters used
The filters currently being used by other telescopes or organizations.
Units of measurements:
* Ã… =
Ångström
* nm =
nanometre
* μm =
micrometre
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer ( American spelling), also commonly known as a micron, is a unit of length in the International System of ...
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,