page_title: Astronomical filter
section_title: Color filters
hierarchical_section_title: Astronomical filter / Color filters
caption_attribution_description: Filter KB20
context_page_description: An astronomical filter is a telescope accessory consisting of an optical filter used by amateur astronomers to simply improve the details of celestial objects, either for viewing or for photography. Research astronomers, on the other hand, use various band-pass filters for photometry on telescopes, in order to obtain measurements which reveal objects' astrophysical properties, such as stellar classification and placement of a celestial body on its Wien curve.
  Most astronomical filters work by blocking a specific part of the color spectrum above and below a bandpass, significantly increasing the signal to noise ratio of the interesting wavelengths, and so making the object gain detail and contrast. While the color filters transmit certain colors from the spectrum and are usually used for observation of the planets and the Moon, the polarizing filters work by adjusting the brightness, and are usually used for the Moon. The broad-band and narrow-band filters transmit the wavelengths that are emitted by the nebulae, and are frequently used for reducing light pollution.
context_section_description: Color filters work by absorption/transmission, and can tell which part of the spectrum they are reflecting and transmitting. Filters can be used to increase contrast and enhance the details of the Moon and planets. All of the visible spectrum colors each have a filter, and every color filter is used to bring a certain lunar and planetary feature; for example, the #8 yellow filter is used to show Mars's maria and Jupiter's belts.
  The Wratten system is the standard number system used to refer to the color filter types. It was first manufactured by Kodak in 1909.
  Professional filters are also colored, but their bandpass centers are placed around other midpoints (such as in the UBVRI and Cousins systems).
  Some of common color filters and their uses are:
  Chromatic aberration filters: Used for reduction of the purplish halo, caused by chromatic aberration of refracting telescopes. Such halo can obscure features of bright objects, especially Moon and planets. These filters have no effect on observing faint objects.
  Red: Reduces sky brightness, particularly during daylight and twilight observations. Improves definition of maria, ice, and polar areas of Mars. Improves contrast of blue clouds against background of Jupiter and Saturn.
  Deep yellow: Improves resolution of atmospheric features of Venus, Jupiter (especially in polar regions), and Saturn. Increases contrast of polar caps, clouds, ice and dust storms on Mars. Enhances comet tails.
  Dark green: Improves cloud patterns on Venus. Reduces sky brightness during daylight observation of Venus. Increases contrast of ice and polar caps on Mars. Improves visibility of the Great Red Spot on Jupiter and other features in Jupiter atmosphere. Enhances white clouds and polar regions on Saturn.
  Medium blue: Enhances contrast of Moon. Increases contrast of faint shading of Venus clouds. Enhances surface features, clouds, ice and dust storms on Mars. Enhances definition of boundaries between features in atmospheres of Jupiter and Saturn. Improves definition of comet gas tails.
caption: A blue color filter
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