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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).
The "Air Almanac" of the United States and Great Britain tabulates celestial coordinates for 10-minute intervals for use in aerial navigation. The Sokkia Corporation's annual "Celestial Observation Handbook and Ephemeris" tabulated daily celestial coordinates (to a tenth of an arcsecond) for the Sun and nine stars; it was last published for 2008.
Two sample pages of the 2002 Nautical Almanac. The Nautical Almanac has been the familiar name for a series of official British almanacs published under various titles since the first issue of The Nautical Almanac and Astronomical Ephemeris, for 1767: [1] this was the first nautical almanac to contain data dedicated to the convenient determination of longitude at sea.
The American Ephemeris and Nautical Almanac was published for the years 1855 to 1980, containing information necessary for astronomers, surveyors, and navigators. It was based on the original British publication, The Nautical Almanac and Astronomical Ephemeris, with which it merged to form The Astronomical Almanac, published from the year 1981 to the present.
His Majesty's Nautical Almanac Office (HMNAO), now part of the United Kingdom Hydrographic Office, was established in 1832 on the site of the Royal Observatory, Greenwich (ROG), where The Nautical Almanac had been published since 1767. HMNAO produces astronomical data for a wide range of users, such as astronomers, mariners, aviators, surveyors ...
In 1849, the Nautical Almanac Office (NAO) was established in Cambridge, Massachusetts as a separate organization. In 1866, it was moved to Washington, D.C. , operating near Fort Myer. It relocated to the U.S. Naval Observatory grounds in 1893.
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,
From 1865 to 1884, the Bureau was responsible for the Office of Detail, which handled the assignment and detailing of naval officers. That Office had been established in March 1861, just prior to the outbreak of the Civil War, in the Office of the Secretary of the Navy. The Office of Detail reverted to the Secretary's office on October 1, 1884 ...