GMT
Greenwich Mean Time (GMT) is the mean solar time at the Royal Greenwich Observatory in Greenwich near London, England, which by convention is at 0 degrees geographic longitude. Theoretically, noon Greenwich Mean Time is the moment when the Sun crosses the Greenwich meridian (and reaches its highest point in the sky in Greenwich). Because of the Earth's uneven speed in its elliptic orbit, this event may be up to 16 minutes off apparent solar time (known as the analemma); but this is averaged out over the year through the use of the mean sun.
The daily rotation of the Earth is somewhat irregular (see Delta-T) and is slowing down.
Therefore, GMT is not used as official clock time anymore. Nowadays, the official clock time is measured by atomic clocks and is known as Coordinated Universal Time (UTC). By using leap seconds, UTC is kept within 0.9 seconds from GMT.
Hourly time signals from Greenwich Observatory were first broadcasted on February 5, 1924.
See also sidereal time, solar time, BPM, CHU, VNG, WWV
Referenced By
1894 | 1924 | 2001 Coalition Attack on Afghanistan/Timeline October 2001 | 2001 U.S. Attack on Afghanistan/Timeline October 2001 | 2001 U.S. Attack on the Taliban/Timeline October 2001 | Abdul Ahad Mohmand | Aerospatiale-BAC Concorde | Age of Earth | Age of the Earth | Amelia Earhart | Bodzinka | Bojinca | Bojinga | Bojinga Project | Bojinga plot | Bojinka | Bojinka Plot | Bojinka Project | Calculating local time | Concorde | H2G2 | Japan Standard Time | Khaled Sheikh Bojinka | Khalid Shaikh Bojinka | Korea standard time | List of TLAs | METAR | May 2003 | Operation Bodzinka | Operation Bojinca | Operation Bojinga | Operation Bojinka | Project Bodzinka | Project Bojinca | Project Bojinga | Project Bojinka | QSL card | September 11, 2001 Attacks Timeline for September | September 11, 2001 Terrorist Attack/Timeline September 2001 | September 11, 2001 Terrorist Attacks Timeline for September | TLAs from EAA to HZZ | Three-letter abbreviation | Three-letter acronym | Three Letter Abbreviation | Three Letter Acronym | Time Zone | Time zones | Timeline of U.S. attack on Afghanistan in October 2001 | Timezone | Yang Liwei
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