greenwich mean time is the time difference between utc and gmt.
greenwich mean time is the time difference between utc and gmt.
what is the time difference between utc and gmt?
greenwich mean time
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the purpose of a chronometer is to measure accurately the time of a known fixed location, for example greenwich mean time (gmt). this is particularly important for navigation. knowing gmt at local noon allows a navigator to use the time difference between the ship's position and the greenwich meridian to determine the ship's longitude. as the earth rotates at a regular rate, the time difference between the chronometer and the ship's local time can be used to calculate the longitude of the ship relative to the greenwich meridian (defined as 0°) using spherical trigonometry. in modern practice, a nautical almanac and trigonometric sight-reduction tables permit navigators to measure the sun, moon, visible planets, or any of 57 selected stars for navigation at any time that the horizon is visible.
marine chronometer