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).
Time zones
To convert from GMT add the value shown in the table below for the local time zone. Convert to GMT by subtracting the value.
| Time Zone | Offset | Daylight Savings | |
|---|---|---|---|
| EST (New York) | -5 hours | EDT | -4 hours |
| CST (Chicago) | -6 hours | CDT | -5 hours |
| MST (Denver) | -7 hours | MDT | -6 hours |
| PST (Los Angeles) | -8 hours | PDT | -7 hours |
For all of Greater China, GMT remains 7 hours before Beijing time all year around. Thus, 7 AM in Beijing is midnight in Greenwich mean time. While daylight saving time (DST) is in force for the United States, the time in Beijing is exactly twelve hours ahead of New York time.
History
On January 1, 1925, the reference point for the start of the day (zeroth hour) was changed from noon to midnight and it was recommended that the term "Universal Time" should be used for the new GMT.[1]
References
- ↑ Greenwich Mean Time at the Free On-Line Dictionary Of Computing. 2001-08-02.
External links
- What is Greenwich Mean Time? at Royal Museums Greenwich
- Greenwich Mean Time at Wikipedia
