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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 ...
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).
The color perceived is similar to that presented by a monochromatic blue (at wavelength 474–476 nm) mixed with white light, that is, an unsaturated blue light. [5] The explanation of blue color by Lord Rayleigh in 1871 is a famous example of applying dimensional analysis to solving problems in physics. [6]
Blue hour at the Old Cathedral of the Holy Name of Jesus, Bragança in Portugal. The blue hour (from French l'heure bleue; [1] [a] pronounced [lœʁ blø]) is the period of twilight (in the morning or evening, around the nautical stage) when the Sun is at a significant depth below the horizon.
The color temperature of daylight varies with the time of day. It tends to be around 2,000 K shortly after sunrise or before sunset, around 3,500 K during "golden hour", and around 5,500 K at midday. The color temperature can also change significantly with altitude, latitude, season, and weather conditions.
When weather systems predominantly move from west to east, a red sky at night indicates that the high pressure air (and better weather) is westwards. In the morning the light is eastwards, and so a red sky then indicates the high pressure (and better weather) has already passed, and an area of low pressure is following behind. [11] A red sunrise.
Finally, night occurs when the Sun reaches 18 degrees below the horizon and no longer illuminates the sky. [4] Locations further north than the Arctic Circle and further south than the Antarctic Circle experience no full sunset or sunrise on at least one day of the year, when the polar day or the polar night persists continuously for 24 hours ...
Zodiacal light seen behind the Submillimeter Array from the summit of Mauna Kea. In the mid-latitudes, the zodiacal light is best observed in the western sky in the spring after the evening twilight has completely disappeared, or in the eastern sky in the autumn just before the morning twilight appears.