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 ...

, a photometric system is a set of well-defined

passband A passband is the range of frequencies or wavelengths that can pass through a filter. For example, a radio receiver contains a bandpass filter to select the frequency of the desired radio signal out of all the radio waves picked up by its antenn ...

s (or

optical filter An optical filter is a device that selectively transmits light of different wavelengths, usually implemented as a glass plane or plastic device in the optical path, which are either dyed in the bulk or have interference coatings. The optical ...

s), 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 fro ...

; 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 radiation ...

(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 Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

(NIR) and part of mid-infrared (MIR). The letters are not standards, but are recognized by common agreement among

astronomers An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either obse ...

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 a ...

. 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. Example of use of J for "near-infrared"

Filters used

The filters currently being used by other telescopes or organizations. Units of measurements: * Å =

Ångström The angstromEntry "angstrom" in the Oxford online dictionary. Retrieved on 2019-03-02 from https://en.oxforddictionaries.com/definition/angstrom.Entry "angstrom" in the Merriam-Webster online dictionary. Retrieved on 2019-03-02 from https://www.m ...

* nm =

nanometre 330px, Different lengths as in respect to the molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re ...

* μm =

micrometre The micrometre (American and British English spelling differences#-re, -er, international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American and British English spelling differences# ...

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,

Photometric letters

Filters used

See also

References and footnotes

External links