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| 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. | 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 ], ]. | ||
| Critics of GMT argue that the assignment of only 1 day to the Earth's rotation, with a 24-hour difference occurring at the International Date Line, is an erroneous conceptualisation. In particular, ] shows that there are in fact 4 simultaneous days in a single rotation of Earth. | |||
| ''See also'' ], ], ], ], ], ] | ''See also'' ], ], ], ], ], ] | ||
Revision as of 05:32, 2 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.
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.
Critics of GMT argue that the assignment of only 1 day to the Earth's rotation, with a 24-hour difference occurring at the International Date Line, is an erroneous conceptualisation. In particular, Time Cube shows that there are in fact 4 simultaneous days in a single rotation of Earth.
See also sidereal time, solar time, BPM, CHU, VNG, WWV