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  5. /Astronomy: General
  6. / Greenwich mean time

Greenwich mean time

Greenwich mean timeorGreenwich meridian time(GMT), the former name for mean solar time at the site of the Royal Observatory in Greenwich, England, which is located on theprime meridian. In 1925 the numbering system was changed to make GMT equivalent tocivil timeat the prime meridian, and in 1928 the International Astronomical Union changed the designation of thestandard timeof the prime meridian touniversal time(UT), which is now in general use.

    The Columbia Electronic Encyclopedia,6th ed. Copyright © 2022, Columbia University Press. All rights reserved.

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