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For example, the solar elevation angle is: 90° at the subsolar point, which occurs, for example, at the equator on a day of equinox at solar noon; near 0° at the sunset or at the sunrise; between −90° and 0° during the night (midnight) An exact calculation is given in position of the Sun. Other approximations exist elsewhere. [6]
Also, unlike most other solar measurements, sunrise occurs when the Sun's upper limb, rather than its center, appears to cross the horizon. The apparent radius of the Sun at the horizon is 16 arcminutes. [1] These two angles combine to define sunrise to occur when the Sun's center is 50 arcminutes below the horizon, or 90.83° from the zenith. [1]
It is the complement to the solar altitude or solar elevation, which is the altitude angle or elevation angle between the sun’s rays and a horizontal plane. [4] [5] At solar noon, the zenith angle is at a minimum and is equal to latitude minus solar declination angle. This is the basis by which ancient mariners navigated the oceans. [6]
is the solar hour angle at either sunrise (when negative value is taken) or sunset (when positive value is taken); ϕ {\displaystyle \phi } is the latitude of the observer on the Earth ; δ {\displaystyle \delta } is the sun declination .
Similar equations are coded into a Fortran 90 routine in Ref. [3] and are used to calculate the solar zenith angle and solar azimuth angle as observed from the surface of the Earth. Start by calculating n , the number of days (positive or negative, including fractional days) since Greenwich noon, Terrestrial Time, on 1 January 2000 ( J2000.0 ).
The solar azimuth angle is the azimuth (horizontal angle with respect to north) of the Sun's position. [ 1 ] [ 2 ] [ 3 ] This horizontal coordinate defines the Sun 's relative direction along the local horizon , whereas the solar zenith angle (or its complementary angle solar elevation ) defines the Sun's apparent altitude .
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The degree of polarization first increases with increasing distance from the Sun, and then decreases away from the Sun. Thus, the maximum degree of polarization occurs in a circular band 90° from the Sun. In this band, degrees of polarization near 80% are typically reached. Degree of polarization in the Rayleigh sky at sunset or sunrise. The ...