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Time on a ship's clocks and in a ship's log had to be stated along with a "zone description", which was the number of hours to be added to zone time to obtain GMT, hence zero in the Greenwich time zone, with negative numbers from −1 to −12 for time zones to the east and positive numbers from +1 to +12 to the west (hours, minutes, and ...
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.
[8]: 10 [9] The most common chart size was early established as the "Double-elephant", about 39 X 25.5 inches, and this has continued to be the case. [10] Chart design gradually simplified over the years, with less detail on land, focusing on features visible to the mariner. Contours were increasingly used for hills instead of hatching.
If present, a dagger (†) indicates the usage of a nautical time zone letter outside of the standard geographic definition of that time zone. Some zones that are north/south of each other in the mid-Pacific differ by 24 hours in time – they have the same time of day but dates that are one day apart. The two extreme time zones on Earth (both ...
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.
Such designations can be ambiguous; for example, "CST" can mean China Standard Time (UTC+08:00), Cuba Standard Time (UTC−05:00), and (North American) Central Standard Time (UTC−06:00), and it is also a widely used variant of ACST (Australian Central Standard Time, UTC+9:30). Such designations predate both ISO 8601 and the internet era; in ...
OpenSeaMap is a software project collecting freely usable nautical information and geospatial data to create a worldwide nautical chart. This chart is available on the OpenSeaMap website, and can also be downloaded for use as an electronic chart for offline applications. [1] The project is part of OpenStreetMap. OpenSeaMap is part of the ...
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.