Greenwich mean time (redirected from Greenwich Time)

Greenwich mean time or Greenwich meridian time (GMT), the former name for mean solar time at the original site of the Royal Observatory in Greenwich, England, which is located on the prime meridian. In 1925 the numbering system was changed to make GMT equivalent to civil time at the prime meridian, and in 1928 the International Astronomical Union changed the designation of the standard time of the prime meridian to universal time (UT), which is now in general use.

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Greenwich Mean Time (GMT)

Former name for mean solar time of the longitude (0°) of the former Royal Observatory at Greenwich, England, or Greenwich meridian. GMT was used to avoid potentially confusing references to local time systems (zones). In accord with tradition, 0000 GMT (denoting the start of a solar day) occurred at noon. In 1925 the numbering system for GMT was changed so that the day (like the civil day) began at midnight. Some confusion resulted, and in 1928 the International Astronomical Union changed the designation of the standard time of the zero meridian to Universal Time, which remains in general use. The term GMT is still used for some purposes (including navigation) in English-speaking countries.

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Greenwich Mean Time, Greenwich Time

mean solar time on the 0? meridian passing through Greenwich, England, measured from midnight: formerly a standard time in Britain and a basis for calculating times throughout most of the world, it has been replaced by an atomic timescale

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Greenwich mean time [′gren·ich ′mēn ¦tīm]

(astronomy)

Mean solar time at the meridian of Greenwich. Abbreviated GMT. Also known as Greenwich civil time; universal time; Z time; zulu time.

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(time, standard)

Greenwich Mean Time - (GMT) The local time on the Greenwich meridian, based on the hypothetical mean sun (which averages out the effects of the Earth's elliptical orbit and its tilted axis). GMT is the basis of the civil time for the UK. In 1925 the reference point was changed from noon to midnight and it was recommended that the term "Universal Time" should be used for the new GMT. Authorities disagreed on whether GMT equates with UT0 or UT1, however the differences between the two are of the order of thousandths of a second. GMT is no longer used for scientific purposes.