| Revision as of 00:38, 3 February 2004 editArchivist~enwiki (talk | contribs)289 edits rv← Previous edit | Revision as of 00:39, 3 February 2004 edit undoDysprosia (talk | contribs)28,388 edits don't need esoteric theories in the middle of an articleNext edit → | ||
| Line 2: | Line 2: | ||
| '''Greenwich Mean Time''' ('''GMT''') is the ] at the ] in ] near ], ], which by convention is at 0 degrees geographic ]. Theoretically, noon Greenwich Mean Time is the moment when the ] crosses the Greenwich ] (and reaches its highest point in the sky in Greenwich). Because of the Earth's uneven speed in its elliptic ], this event may be up to 16 minutes off ] (known as the ]); but this is averaged out over the ] through the use of the ]. | '''Greenwich Mean Time''' ('''GMT''') is the ] at the ] in ] near ], ], which by convention is at 0 degrees geographic ]. Theoretically, noon Greenwich Mean Time is the moment when the ] crosses the Greenwich ] (and reaches its highest point in the sky in Greenwich). Because of the Earth's uneven speed in its elliptic ], this event may be up to 16 minutes off ] (known as the ]); but this is averaged out over the ] through the use of the ]. | ||
| The daily rotation of the Earth is somewhat irregular (see ]) and is slowing down. | |||
| Therefore, GMT is not used as official clock time anymore. Nowadays, the official clock time is measured by ]s and is known as ] (UTC). By using ]s, UTC is kept within 0.9 seconds from GMT. | |||
| Hourly time signals from Greenwich Observatory were first broadcasted on ], ]. | Hourly time signals from Greenwich Observatory were first broadcasted on ], ]. | ||
| ''See also'' ], ], ], ], ], ] | ''See also'' ], ], ], ], ], ], ] | ||
Revision as of 00:39, 3 February 2004
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.
Hourly time signals from Greenwich Observatory were first broadcasted on February 5, 1924.
See also sidereal time, solar time, BPM, CHU, VNG, WWV, Time Cube