Greenwich Mean Time (GMT)

Clock time and time zone standard

GMT stays the same all year round

Time at the Shepherd Gate Clock, at the Royal Observatory in Greenwich, UK

Greenwich Mean Time is two things

  • Greewich Mean Time = mean or average solar time at the Prime Meridian (0 degrees longitude)

    At noon, when the sun is straight above Greenwich meridian, the clock at the Royal Observatory shows 12.00.

    The word 'mean' is used to point out that GMT is an average of all the values recorded throughout a year.

    This is due to the specifics of the Earth's movement round its axis and round the Sun.

    Find out more about the history of GMT in this article

  • GMT is also the name of a time zone, used in UK and several other countries.

    Clocks in the UK will show GMT only when Daylight Saving (DST) is not in use.

    When DST is in use, between March and October, the clocks are on British Summer Time (BST), or GMT+1.

    The United Kingdom is in the Western European Time Zone.

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