In astronomy, background commonly refers to the incoming light from an apparently empty part of the night sky. Even if no visible astronomical objects are present in given part of the sky, there always is some low luminosity present, due mostly to light diffusion from the atmosphere (diffusion of both incoming light from nearby sources, and of man-made Earth sources like cities). In the visible band, luminosity level is around the 22nd magnitude per square-arcsecond: a very low level, but anyway well within the limits of the current generation of telescopes. The Hubble Space Telescope does not suffer from this problem.
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| - Background (astronomy) (en)
- 背景 (天文) (zh)
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| - In astronomy, background commonly refers to the incoming light from an apparently empty part of the night sky. Even if no visible astronomical objects are present in given part of the sky, there always is some low luminosity present, due mostly to light diffusion from the atmosphere (diffusion of both incoming light from nearby sources, and of man-made Earth sources like cities). In the visible band, luminosity level is around the 22nd magnitude per square-arcsecond: a very low level, but anyway well within the limits of the current generation of telescopes. The Hubble Space Telescope does not suffer from this problem. (en)
- 背景，在天文學中通常是指來自看起來空無一物的夜晚天空部分中的光線。 即使沒有可見的天體存在於給定的天空部分中，但那裏總是會有一些低亮度的光存在著，它們大多數是來自地球大氣層的（漫射光來自附近的光源和人造的地球光源，像是城市的燈光）。在可見光的波段，每平方角秒的亮度相當於視星等的22等：非常低的亮度，但不管怎樣，都在這一代望遠鏡的極限星等範圍內。哈伯太空望遠鏡一樣不能倖免於這個問題的影響。 在紅外線天文學，這個問題更為嚴重：由於包含較長的波長，天空和望遠鏡本身就是光源。解決這個問題的變通辦法是，紅外線望遠鏡通常使用一種稱為的技術，鏡子在感興趣的天體和附近空的天空之間迅速的擺動。將這兩個影像互減，希望只有留下來自光源的影像。 夜空的亮度有幾個貢獻的來源，其中有些來自儀器，通常都是來自地基的儀器，或是大氣層中原本就存在的（像是氣輝）。即使我們能將儀器和大氣層中元件（像是使用中的航太機具）的效應降至最低，仍有幾個天體會為背景做出貢獻：這些可能是像小行星這種點光源、銀河系的恆星、距離遙遠的星系，以及瀰漫性的來源，如太陽系、銀河系和星系空間中的塵埃。 實際的波長和的重要性取決於測量儀器的特性。主要的測量的波長取決於特定的元件的實際重要性。由天文物理元件造成的背景所引起測量上的不確定性（或噪音）稱為。 (zh)
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| - In astronomy, background commonly refers to the incoming light from an apparently empty part of the night sky. Even if no visible astronomical objects are present in given part of the sky, there always is some low luminosity present, due mostly to light diffusion from the atmosphere (diffusion of both incoming light from nearby sources, and of man-made Earth sources like cities). In the visible band, luminosity level is around the 22nd magnitude per square-arcsecond: a very low level, but anyway well within the limits of the current generation of telescopes. The Hubble Space Telescope does not suffer from this problem. In infrared astronomy, the problem can be much worse: due to the longer wavelengths involved, the sky and the telescope themselves are a source of light. To work around this problem, infrared telescopes often use a technique called , where a mirror rapidly oscillates between the object of interest and the nearby, empty sky. The two images can be subtracted, leaving hopefully only the incoming light from the source. 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 airglow), in the case of ground-based instruments. Even if we able to minimize the effect of instrumental and atmospherical components (e.g. using a spacecraft), there are still several astrophysical 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 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 . In astronomical CCD technology, background 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 the sky is also called a background, and is the sum of the system background level plus the sky's one. A background frame 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. (en)
- 背景，在天文學中通常是指來自看起來空無一物的夜晚天空部分中的光線。 即使沒有可見的天體存在於給定的天空部分中，但那裏總是會有一些低亮度的光存在著，它們大多數是來自地球大氣層的（漫射光來自附近的光源和人造的地球光源，像是城市的燈光）。在可見光的波段，每平方角秒的亮度相當於視星等的22等：非常低的亮度，但不管怎樣，都在這一代望遠鏡的極限星等範圍內。哈伯太空望遠鏡一樣不能倖免於這個問題的影響。 在紅外線天文學，這個問題更為嚴重：由於包含較長的波長，天空和望遠鏡本身就是光源。解決這個問題的變通辦法是，紅外線望遠鏡通常使用一種稱為的技術，鏡子在感興趣的天體和附近空的天空之間迅速的擺動。將這兩個影像互減，希望只有留下來自光源的影像。 夜空的亮度有幾個貢獻的來源，其中有些來自儀器，通常都是來自地基的儀器，或是大氣層中原本就存在的（像是氣輝）。即使我們能將儀器和大氣層中元件（像是使用中的航太機具）的效應降至最低，仍有幾個天體會為背景做出貢獻：這些可能是像小行星這種點光源、銀河系的恆星、距離遙遠的星系，以及瀰漫性的來源，如太陽系、銀河系和星系空間中的塵埃。 實際的波長和的重要性取決於測量儀器的特性。主要的測量的波長取決於特定的元件的實際重要性。由天文物理元件造成的背景所引起測量上的不確定性（或噪音）稱為。 在天文學的CCD技術，背景 通常就是指在沒有光源的情況下，CCD感應器的整體光學系統對入射光的噪音。這些背景可以源自CCD的電子雜訊，來自附近沒有很好遮罩的望遠鏡，或其它的不一而足。對天空中完全空無一物之處的曝光也是背景之一，是系統的背景水平加上天空的總和。 背景系統通常是使用CCD做天文觀測最先接觸到的：在實際的觀測中要先將背景系統從觀測天體的光中扣除掉，在理論上只有來自被觀測天體的光會被導入。 (zh)
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