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Atmospheric refraction becomes more severe when temperature gradients are strong, and refraction is not uniform when the atmosphere is heterogeneous, as when turbulence occurs in the air. This causes suboptimal seeing conditions, such as the twinkling of stars and various deformations of the Sun's apparent shape soon before sunset or after sunrise.
This optical phenomenon occurs because rays of light are strongly bent when they pass through air layers of different temperatures in a steep thermal inversion where an atmospheric duct has formed. [39] A thermal inversion is an atmospheric condition where warmer air exists in a well-defined layer above a layer of significantly cooler air.
Light from the Sun is bent, or refracted, as it enters Earth's atmosphere. This effect causes the apparent sunrise to be earlier than the actual sunrise. Similarly, apparent sunset occurs slightly later than actual sunset. In ordinary atmospheric conditions, the setting or rising Sun appears to be about half a degree above its geometric position.
Looming of the Canadian coast as seen from Rochester, New York, on April 16, 1871. Looming is the most noticeable and most often observed of these refraction phenomena. It is an abnormally large refraction of the object that increases the apparent elevation of the distant objects and sometimes allows an observer to see objects that are located below the horizon under normal conditions.
The distribution of atmospheric seeing through the atmosphere (the C N 2 profile described below) causes the image quality in adaptive optics systems to degrade the further you look from the location of reference star; The effects of atmospheric seeing were indirectly responsible for the belief that there were canals on Mars.
As one of the three principal factors governing astronomical seeing (the others being light pollution and cloud cover), atmospheric scintillation is defined as variations in illuminance only. In simple terms, twinkling of stars is caused by the passing of light through different layers of a turbulent atmosphere.
The Cherenkov light emitted from patient's tissue during radiation therapy is a very low light level signal but can be detected by specially designed cameras that synchronize their acquisition to the linear accelerator pulses. [31] The ability to see this signal shows the shape of the radiation beam as it is incident upon the tissue in real ...
Lunar corona A solar corona up Beinn Mhòr (South Uist). In meteorology, a corona (plural coronae) is an optical phenomenon produced by the diffraction of sunlight or moonlight (or, occasionally, bright starlight or planetlight) [1] by individual small water droplets and sometimes tiny ice crystals of a cloud or on a foggy glass surface.