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Ultralight vehicles may be operated during the twilight periods 30 minutes before official sunrise and 30 minutes after official sunset or, in Alaska, during the period of civil twilight as defined in the Air Almanac, if: The vehicle has an operating anti-collision light visible for at least 3 statute miles [1]
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,
In the US, civil twilight for aviation is defined in Part 1.1 of the Federal Aviation Regulations (FARs) [8] as the time listed in the American Air Almanac. [ 9 ]
Civil polar twilight occurs at latitudes between about 67°24' and 72°34' North or South, where the Sun will be below the horizon all day on the winter solstice, but by less than 6° at solar noon. There is then no true daylight at the solar culmination, only civil twilight. During civil polar twilight, there is still enough light for most ...
In aviation, "night" is defined as the period from "the end of evening civil twilight to the beginning of morning civil twilight". [1]: 19 [2] In EASA states and the United Kingdom, the requirements for a night rating for aeroplanes are: [1]: FCL.810 [3] theoretical instruction
As an example, the Astronomical Almanac for the Year 2017 gave the ERA at 0 h 1 January 2017 UT1 as 100° 37′ 12.4365″. [13] Since Coordinated Universal Time (UTC) is within a second or two of UT1, this can be used as an anchor to give the ERA approximately for a given civil time and date.
Before the fourth season was set to air in 1962, the show was unable to find a sponsor, according to the book A Critical History of Television's The Twilight Zone.
Twilight (both dusk and dawn) is divided into three 6° segments that mark the Sun's position below the horizon. At civil twilight, the center of the Sun's disk appears to be between 1/4° and 6° below the horizon. At nautical twilight, the Sun's altitude is between –6° and –12°. At astronomical twilight, the Sun is between –12° and ...