The term Greenwich Mean Time is still used to represent the civil time in Britain. The way Greenwich Mean Time (GMT) works is a little bit different from standard time zones such as EST or PST or daylight time zones such as CDT or EDT. The main difference is that Greenwich Mean Time doesn’t have an offset from Coordinated Universal Time (UTC).
Surprisingly, GMT watches aren’t made with the usual 24-hour scale but it’s accompanied by several benefits. In the winter months, local time in the UK is the same as GMT, but in March, local time is moved forward one hour to British Summer Time (BST) until the end of October. These two solutions would help pave the way for GMT to become the worldwide time standard a century later. But each day measured by a clock has the same length, equal to the average (mean) length of a solar day.
At first though, Greenwich time was only really important to astronomers. Therefore, you can choose one, two, or three additional time zones on your watch. It’s a perfect way to observe time together at various time zones without calculating time or using online time converters. Greenwich Mean Time is the “mean” of the everyday time in the year when the Sun crosses the Prime Meridian at the Royal Observatory Greenwich. Therefore, GMT is more of a clock time and not an astronomical time that varies during the year.
GMT and the quest for longitude
It’s a way of standardising and regularising time so we can all know exactly what time it is for our (or anyone’s) location. It is observed in the ACT, COT, CST, ECT, EST, PET during standard time, and in the CDT, EASST during the other months (Daylight saving time). The Shepherd gate clock is considered as the first GMT watch ever that showed the public Greenwich Mean Time. The clock is connected to the Shepherd master clock and was installed at the Royal Observatory Greenwich in 1852. Since it’s masted from far away, the Shepherd gate clock is also called the “slave” clock. There are many major cities in the GMT time zone and in the GMT+1 times zone (Daylight Saving Time).
Mostly, people calculate time based on the Coordinated Universal Time (UTC) which is considered a worldwide standard. GMT is no longer used within the community of scientists but sometimes people still want to find out how GMT works and how to convert it to other time zones. UTC is a time standard that sets the base for time keeping and time zones around the world.
- The Shepherd gate clock is considered as the first GMT watch ever that showed the public Greenwich Mean Time.
- This meant there was no standard timings for when the day would begin and end, or what length an hour might be.
- Even more, from 1866 time was also sent to Harvard University in Cambridge and Massachusetts.
Historically, astronomers used Greenwich Mean Astronomical Time (GMAT), in which the astronomical day began at noon at longitude (0°), in accord with scientific tradition. In 1925 GMT was adopted by astronomers so that the astronomical day began at midnight, the same time as the civil day. Some confusion in terminology resulted, though, and in 1928 the International Astronomical Union changed the designation of the standard time of the Greenwich meridian to Universal Time.
How to Convert GMT to Other Time Zones?
It was the first clock ever to show Greenwich Mean Time directly to the public. It is a ‘slave’ clock, connected to the Shepherd master clock which was installed at the Royal Observatory in 1852. This meant there was no standard timings for when the day would begin and end, or what length an hour might be. As well as Greenwich Mean Time for example, there was also Bristol Mean Time (10 minutes behind GMT) Cardiff Mean Time (13 minutes behind GMT). Greenwich Mean Time is the yearly average (or ‘mean’) of the time each day when the Sun crosses the Prime Meridian at the Royal Observatory Greenwich.
However, in the United Kingdom, GMT is still being used for civil purposes, even though not formally. Each time zone had an offset of a number of hours ahead of GMT or behind GMT, as we’ve explained before. This network of “master” and “slave” clocks was created and installed by Charles Shepherd. Today it’s rather unusual in using the 24-hour dial but originally, it showed astronomical time starting at 12 noon instead of midnight. The most obvious thing about the Shepherd gate clock is that it has 24 hours instead of the usual 12 hours. Therefore, the 12 o’clock hour hand is pointing down rather than upwards.
How did Greenwich Mean Time become the international standard?
Greenwich Mean Time (GMT) has been used to clearly designate epoch by avoiding confusing references to local time systems (zones). This is essentially the same as GMT, but UTC is measured by an atomic clock and is thus more accurate – by split seconds. Greenwich Mean Time (GMT) is the time measured on the Earth’s zero degree line of longitude, or meridian. From that time until 1893, the Shepherd master clock was the heart of Britain’s time system. Its time was sent by telegraph wires to London, Edinburgh, Glasgow, Dublin, Belfast and many other cities.
Where and When is GMT Observed?
In other words, the country that invented GMT is not in GMT time all year round. During summer, the UK is in the BST (British Standard Time) time zone. Generally, if you are in a country east of the Greenwich Meridian, your local time is ahead of GMT (e.g. local time in China is GMT +8 hours). The first was that the USA had already chosen Greenwich as the basis for its own national time zone system. The second was that in the late 19th century, 72% of the world’s commerce depended on sea-charts which used Greenwich as the Prime Meridian. British mariners started keeping at least one chronometer set to GMT.
In fact, it’s used alongside standard time on some continents, including Europe, Africa, North America, and Antarctica. If you know the principles of converting UTC to different time zones, then you can convert GMT as well very easily. There is no time difference between Coordinated Universal Time and Greenwich Mean Time. GMT is officially used in some European and African countries. Interestingly, neither GMT nor UTC change for Daylight Saving Time but some countries that observe GMT switch to different time zones during DST. Since GMT is not a standard time that has an offset from UTC, converting it to other time zones can be a little bit more complicated.
GMT (Greenwich Mean Time) is one of the well-known names of UTC+0 time zone which is 0h. The dividing line between East (GMT+) and West (GMT-) on the opposite side of the world to the Greenwich Meridian is the International Date Line. It was recommended that the meridian line would indicate 0° longitude. The meridian line is marked https://www.dowjonesrisk.com/ by the cross-hairs in the Airy Transit Circle eyepiece. The recommendation was based on the argument that naming Greenwich as Longitude 0º would be of advantage to the largest number of people. GMT was also crucial to the other great solution to the ‘longitude problem’, represented by John Harrison’s famous timekeepers.
The main purpose of Greenwich Mean Time is to standardize time regardless of the location. Until the mid-19th century, almost every town kept its own local time, defined by the Sun. There were no national or international conventions which set how time should be measured. A number of other countries around the world also use this daylight savings measure and change their local times to take advantage of earlier sunrises.
