Greenwich Mean Time (GMT) is often interchanged or confused with Coordinated Universal Time (UTC). By the mid-1850s, almost all public clocks in Britain were set to Greenwich Mean Time and it finally became Britain’s legal standard time in 1880. 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.
- This meant there was no standard timings for when the day would begin and end, or what length an hour might be.
- 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.
- This meant the need for an national time standard became imperative.
- This meant they could calculate their longitude from the Greenwich meridian (longitude 0° by convention).
These two solutions would help pave the way for GMT to become the worldwide time standard a century later. These were tables of ‘lunar distance’ data based on observations at Greenwich and using GMT as the time standard. Greenwich Mean Time (GMT) is the time measured on the Earth’s zero degree line of longitude, or meridian. During Daylight Saving Time the correct time zone is British Summer Time (BST). GMT (Greenwich Mean Time) is one of the well-known names of UTC+0 time zone which is 0h. From that time until 1893, the Shepherd master clock was the heart of Britain’s time system.
How did railways lead to GMT becoming the UK time standard?
This is a modification of the 180° meridian running north to south through the Pacific Ocean. BBC World Service times are normally shown in GMT, although our online schedules will change in March to GMT +1 which is in line with British Summer Time (BST).
Its time was sent by telegraph wires to London, Edinburgh, Glasgow, Dublin, Belfast and many other cities. By 1866, time signals were also sent from the clock to Harvard University in https://www.wallstreetacademy.net/ Cambridge, Massachusetts via the new transatlantic submarine cable. This meant there was no standard timings for when the day would begin and end, or what length an hour might be.
UTC & GMT Library
Greenwich Mean Time (GMT) has been used to clearly designate epoch by avoiding confusing references to local time systems (zones). As the reference for GMT, the Prime Meridian at Greenwich therefore became the centre of world time and the basis for the global system of time zones. However, the 1850s and 1860s saw the expansion of the railway and communications networks.
This meant the need for an national time standard became imperative. 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. 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). In terms of the distribution of accurate time into everyday life, it is one of the most important clocks ever made. 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.
This is essentially the same as GMT, but UTC is measured by an atomic clock and is thus more accurate – by split seconds. 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. Keep track of time with our famous Shepherd Gate clock replica for your wall. It was recommended that the meridian line would indicate 0° longitude. The meridian line is marked by the cross-hairs in the Airy Transit Circle eyepiece. GMT was also crucial to the other great solution to the ‘longitude problem’, represented by John Harrison’s famous timekeepers.
In 1925 GMT was adopted by astronomers so that the astronomical day began at midnight, the same time as the civil day. The term Greenwich Mean Time is still used to represent the civil time in Britain. This 24-hour time standard is kept using highly precise atomic clocks combined with the Earth’s rotation. Here he had the best pendulum clocks installed and set them to the local time. This was Greenwich Mean Time, or the average time when the Sun crossed the meridian at Greenwich. At first though, Greenwich time was only really important to astronomers.
North America
But each day measured by a clock has the same length, equal to the average (mean) length of a solar day. 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. West of the Greenwich Meridian, local time is behind GMT (e.g. local time in New York is GMT -5 hours in winter and GMT -4 hours in summer). This line has been called the Greenwich Meridian since 1884, and it is from here that all terrestrial longitudes are measured and the world’s time zones are calculated. However, some of the countries that use GMT switch to different time zones during their DST period.
The clock originally indicated astronomical time, in which the counting of the 24 hours of each day starts at noon. The clock was changed in the 20th century to indicate Greenwich Mean Time, in which the counting of the 24 hours of each day starts at midnight. It continues to show Greenwich Mean Time and is not adjusted for British Summer Time.
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). British mariners started keeping at least one chronometer set to GMT. This meant they could calculate their longitude from the Greenwich meridian (longitude 0° by convention). 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.
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. Greenwich Mean Time (GMT), the name for mean solar time of the longitude (0°) of the Royal Greenwich Observatory in England. The meridian at this longitude is called the prime meridian or Greenwich meridian.