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The time of dusk is the moment at the very end of astronomical twilight, just before the minimum brightness of the night sky sets in, or may be thought of as the darkest part of evening twilight. [4] However, technically, the three stages of dusk are as follows: At civil dusk, the center of the Sun's disc goes 6° below the horizon in the ...
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Twilight occurs according to the solar elevation angle θ s, which is the position of the geometric center of the Sun relative to the horizon. There are three established and widely accepted subcategories of twilight: civil twilight (nearest the horizon), nautical twilight, and astronomical twilight (farthest from the horizon).
Earth's shadow cast onto the atmosphere can be viewed during the "civil" stage of twilight, assuming the sky is clear and the horizon is relatively unobstructed. The shadow's fringe appears as a dark bluish to purplish band that stretches over 180° of the horizon [3] [4] opposite the Sun, i.e. in the eastern sky at dusk and in the western sky ...
Anticrepuscular rays, or antisolar rays, [1] are meteorological optical phenomena similar to crepuscular rays, but appear opposite the Sun in the sky. Anticrepuscular rays are essentially parallel , but appear to converge toward the antisolar point , the vanishing point , due to a visual illusion from linear perspective .
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Crepuscular rays usually appear orange because the path through the atmosphere at dawn and dusk passes through up to 40 times as much air as rays from a high Sun at noon. Particles in the air scatter short-wavelength light (blue and green) through Rayleigh scattering much more strongly than longer-wavelength yellow and red light.
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