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Scientifically precise local time varies with longitude: a difference of 15° longitude corresponds to a one-hour difference in local time, due to the differing position in relation to the Sun. Comparing local time to an absolute measure of time allows longitude to be determined. Depending on the era, the absolute time might be obtained from a ...
Time sight is a general method for determining longitude by celestial observations using a chronometer; these observations are reduced by solving the navigational triangle for meridian angle and require known values for altitude, latitude, and declination; the meridian angle is converted to local hour angle and compared with Greenwich hour angle.
Time zones of the world. A time zone is an area which observes a uniform standard time for legal, commercial and social purposes. Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude, because it is convenient for areas in frequent communication to keep the same time.
Longitude calculations can be simplified using a clock is set to the local time of a starting point whose longitude is known, transporting it to a new location, and using it for astronomical observations. The longitude of the new location can be determined by comparing the difference of local mean time and the time of the transported clock.
Local mean time (LMT) is a form of solar time that corrects the variations of local apparent time, forming a uniform time scale at a specific longitude. This measurement of time was used for everyday use during the 19th century before time zones were introduced beginning in the late 19th century; it still has some uses in astronomy and ...
This is an accepted version of this page This is the latest accepted revision, reviewed on 14 February 2025. System to specify locations on Earth For broader coverage of this topic, see Spatial reference system. Longitude lines are perpendicular to and latitude lines are parallel to the Equator. Geodesy Fundamentals Geodesy Geodynamics Geomatics History Concepts Geographical distance Geoid ...
In geodesy, conversion among different geographic coordinate systems is made necessary by the different geographic coordinate systems in use across the world and over time. Coordinate conversion is composed of a number of different types of conversion: format change of geographic coordinates, conversion of coordinate systems, or transformation ...
Knowing Greenwich time and local time, the navigator can work out longitude. [1] Local time can be determined from a sextant observation of the altitude of the Sun or a star. [8] [9] Then the longitude (relative to Greenwich) is readily calculated from the difference between local time and Greenwich Time, at 15 degrees per hour of difference.