Nautical Almanac

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The Nautical Almanac (Nautical almanac and astronomical ephemeris) is an astronomical yearbook of around 300 pages specially designed for rapid astronavigation at sea. The first almanac of the British Royal Greenwich Observatory appeared in 1767 and was the first available means of determining the longitude on ships from measured lunar distances . Tables for the sun and planets were soon added.

The almanac is published one year in advance and contains hourly ephemeris for the sun , moon and the five bright planets , the daily apparent star locations of 57 navigation stars and information about twilight. It is designed for an accuracy of 0.1 ′ ( minutes of arc ), which is sufficient for nautical purposes and time-consuming interpolations of the table values ​​are unnecessary. The time correction dUT1 can also be omitted because the coordinates apply to a precalculated earth rotation (UT1).

Until the middle of the 20th century , the almanac was a more extensive yearbook that many states and institutes published independently (e.g. Heidelberg and Berlin Astronomical Yearbooks ). When this multiple redundant work was replaced by international cooperation, the “fast-track procedures” remained with the Nautical Almanac, while a large part of the more precise projections went to the Heidelberg Institute (see Astronomical Calculation Institute and FK5 ).

The Nautical Almanac appears in two identical editions for the United Kingdom and the United States ( Nautical Almanac Offices HM, London Secretary of State, and United States Naval Observatory , Washington), as well as licensed editions for around ten other languages.

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  1. ↑ 0.1 arc minutes are 6 ″ (arc seconds), which corresponds to 0.4 s (time seconds).

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