Showing posts with label GMT. Show all posts
Showing posts with label GMT. Show all posts

Dec 9, 2016

More About Time Zones

Prior to standardization, there were thousands of local times around the world, generally based on the Sun’s position at a given time. Even after clocks became somewhat commonplace, two cities a short distance apart sometimes had very different ideas about what time it was at any given moment. Usually, the accepted time for a given city was based on a well-known clock in the town, like a clock tower, which was often at least partially based on the Sun’s position.

Once people began to travel, establishing a universal time became more important. During 1675 the GMT was invented at the Royal Observatory at Greenwich, England. As transportation and communication continued to advance, the need to have standard timekeeping became increasingly apparent. During 1840, the Great Western Railway in Great Britain adopted GMT (Greenwich Mean Time) as the standard for its schedule, and by 1847, all British rail companies were using GMT, which was also called Railway Time.
The Royal Observatory began telegraphing time signals in 1852, and by 1855, 98% of the public clocks in Great Britain were displaying GMT, either alone or in conjunction with local time.
Sir Sandford Fleming was the instigator of a single, worldwide system of timekeeping. His basic idea of having a universal day beginning at Greenwich was ultimately adopted at the International Meridian Conference in 1884. The conferees decided that the line of longitude that passed through Greenwich would be the prime meridian where each universal day would begin at midnight.

As had once been the case in Europe, and for some semblance of standardization from town to town, railroad companies set their own times, which differed from company to company. William F. Allen’s proposal was adopted by the US rail system on November 18, 1883. It was called the day of two noons, every railroad station clock was reset to reflect new time zones, which were designated Intercolonial, Eastern, Central, Mountain, and Pacific.
Less than one hundred years ago, the US Congress passed the Standard Time Act in 1918, which established a single, standard system of timekeeping for the entire country and designated its five time zones by reference to the Greenwich meridian.
Incidentally, it is called “Greenwich Mean Time,” because the Earth’s daily rotation time is slightly irregular, causing a variance of about plus or minus 16 minutes, so to be consistent, the mean time is used.

Nov 25, 2016


Greenwich Mean Time (GMT) is often confused with Coordinated Universal Time (UTC). GMT and UTC share the same current time in practice, but there is a basic difference between the two. GMT is a time zone and UTC is a time standard.

GMT is a time zone officially used in some European, African, and other countries. The time can be displayed using both the 24-hour format (0 - 24) or the 12-hour format (1 - 12 am/pm).

UTC is not a time zone, but a time standard that is the basis for civil time and time zones worldwide. This means that no country or territory officially uses UTC as a local time.

Neither UTC nor GMT ever change for Daylight Saving Time. However, some of the countries that use GMT switch to different time zones during their Daylight Saving Time periods. For example, the United Kingdom is not on GMT all year, it uses British Summer Time (BST), which is one hour ahead of GMT, during the summer months. Seems to me all Daylight Saving Time should adopt the British acronym and call it for what it is - BST, for Bull S... Time.