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is usually referred to the overall optical "noise" of the system, that is, the incoming light on the CCD sensor in absence of light sources. This background can originate from electronic noise in the CCD, from not-well-masked lights nearby the telescope, and so on. An exposure on an empty patch of
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components contributing to the sky background: these could be sets of point sources like faint asteroids, Galactic stars and far away galaxies, as well as diffuse sources like dust in the Solar System, in the Milky Way, and in the intergalactic space. The actual importance of a specific component
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is often the first exposure in an astronomical observation with a CCD: the frame will then be subtracted from the actual observation result, leaving in theory only the incoming light from the astronomical object being observed.
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depends mostly of the wavelength of the measurement. The uncertainty (or noise) of the measurements caused by the astrophysical components of the sky background is called
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There are several sources which contribute to the brightness of the (night) sky. Some of these are instrumental, or due to the presence of the atmosphere (like the
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involved, the sky and the telescope themselves are a source of light. To work around this problem, infrared telescopes often use a technique called
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Even if no visible astronomical objects are present in given part of the sky, there always is some low luminosity present, due mostly to
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the sky is also called a background, and is the sum of the system background level plus the sky's one.
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commonly refers to the incoming light from an apparently empty part of the night
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