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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.
A marine chronometer is a precision timepiece that is carried on a ship and employed in the determination of the ship's position by celestial navigation.It is used to determine longitude by comparing Greenwich Mean Time (GMT), and the time at the current location found from observations of celestial bodies.
Time: A major change introduced with the 1960 issue of The Astronomical Ephemeris was the use of ephemeris time in place of mean solar time for the major ephemeris tabulations. [12] But the Nautical Almanac, now continuing as a separate publication addressed largely to navigators, continued to give tabulations based on mean solar time (UT).
Since the 1920s, a nautical standard time system has been in operation for ships on the high seas. As an ideal form of the terrestrial time zone system, nautical time zones consist of gores of 15° offset from GMT by a whole number of hours. A nautical date line follows the 180th meridian, bisecting one 15° gore into two 7.5° gores that ...
The 15° gore that is offset from GMT or UT1 (not UTC) by twelve hours is bisected by the nautical date line into two 7.5° gores that differ from GMT by ±12 hours. In reality nautical time zones are used only for radio communication etc. Internally on the ship, e.g. for work and meal hours, the ship may use a suitable time of its own choosing.
Using the Equation of time correction along with the time averaged ascending/descending noon sights can result in accuracies of 1 nautical mile (1.9 km) or less. Without time averaging, the difficulties in determining the exact moment of local noon due to the flattening of the Sun’s arc across the sky reduce the accuracy of calculation.
Knowing the time of the observation, and with the data contained in the nautical calendar, it is possible to determine the astronomical coordinates of the observed star. Knowing the coordinates of the observed star and the height above the horizon with which it was observed, we can deduce that the observer's position is located on a circle ...
A nautical almanac is a publication describing the positions of a selection of celestial bodies for the purpose of enabling navigators to use celestial navigation to determine the position of their ship while at sea.