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Nautical twilight has military considerations as well. The initialisms BMNT (begin morning nautical twilight, i.e. nautical dawn) and EENT (end evening nautical twilight, i.e. nautical dusk) are used and considered when planning military operations. A military unit may treat BMNT and EENT with heightened security, e.g. by "standing to", for ...
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.
Three different concepts of "night" are referred to in the Federal Aviation Regulations in the US. These include the periods from sunset to sunrise - used for nav lights,; the end of evening civil twilight to the beginning of morning civil twilight (this is the "standard definition of night", given in FAR Section 1.1) - used for logging night flight,
Civil, nautical, and astronomical twilight. [3] Dusk is the darkest part of evening twilight. 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]
Evening is the period of a day that begins at the end of daylight and overlaps with the beginning of night. [1] It generally indicates the period of time when the sun is close to the horizon and comprises the periods of civil, nautical and astronomical twilight. The exact times when evening begins and ends are subjective and depend on location ...
Nautical time divides the globe into 24 nautical time zones with hourly clock offsets, spaced at 15 degrees by longitudinal coordinate, with no political deviation. Nautical timekeeping dates back to the early 20th century as a standard way to keep time at sea, although it largely only applied to military fleets pre–World War 2.
Nautical twilight begins when there is enough light for sailors to distinguish the horizon at sea, but the sky is still too dark to perform outdoor activities. It begins when the center of the Sun is 12 degrees below the horizon in the morning. Nautical dawn marks the start of nautical twilight, which lasts until civil dawn. [6] [5]
Nautical twilight happens when the Sun is between 6 and 12° below the horizon, so this phenomenon can also be referred to as nautical polar night. Nowhere on mainland Europe is this definition met. The Norwegian town of Longyearbyen, Svalbard, experiences nautical polar twilight from about 11 November until 30 January. Dikson, in Russia