These were tables of ‘lunar distance’ data based on observations at Greenwich and using GMT as the time standard. In 1767 Maskelyne introduced the Nautical Almanac as part of the great 18th century quest to determine longitude. In the 1700s, the fifth Astronomer Royal Nevil Maskelyne brought Greenwich Mean Time to a wider audience. At first though, Greenwich time was only really important to astronomers. This was Greenwich Mean Time, or the average time when the Sun crossed the meridian at Greenwich. Here he had the best pendulum clocks installed and set them to the local time.

Soon after, he was appointed as the first Astronomer Royal and moved into the new Royal Observatory in Greenwich. John Flamsteed came up with the formula for converting solar time to mean time, and published a set of conversion tables in the early 1670s. It wasn’t until the invention of the pendulum clock in the 1650s that it was possible to work out the relationship between mean (clock) time and solar time. Greenwich Mean Time is also the name of the time zone used by some countries in Africa and Western Europe, including in Iceland all year round. Though it has now been replaced by Coordinated Universal Time (UTC), GMT is still the legal time in Britain in the winter, used by the Met Office, Royal Navy and BBC World Service. From 1884 until 1972, GMT was the international standard of civil time. GMT stands for Greenwich Mean Time, the local clock time at Greenwich. Today GMT is reckoned from one midnight to the next.įind out about the Prime Meridian What does GMT stand for? 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. Solar time varies throughout the year, as the time interval between the Sun crossing a set meridian line changes.īut each day measured by a clock has the same length, equal to the average (mean) length of a solar day. In military GMT is known as Zulu time.Greenwich Mean Time was the same as Universal Time (UT), until the introduction of UTC in 1972 a standard astronomical concept used in many technical fields.Essentially, mean time is clock time rather than solar (astronomical) time. It is now often used to refer to Coordinated Universal Time (UTC) when this is viewed as a time zone, and in casual use for the most parts it is the same. Greenwich Mean Time (GMT) originally referred to the mean solar time at the Royal Observatory in Greenwich, London. Other major cities in the area are Abidjan, Dakar, Grand Dakar, Accra Principal Cities: The largest city in the GMT timezone is London from United Kingdom with population about 7.557 million people. Offset: GMT is 0 hours ahead Greenwich Mean Time (GMT) and is used in EuropeĬountries: It is used in following countries: Burkina Faso, Côte d'Ivoire, Britain (UK), Guernsey, Ghana, Greenland, Gambia, Guinea, Guinea-Bissau, Ireland, Isle of Man, Iceland, Jersey, Liberia, Mali, Mauritania, St Helena, Sierra Leone, Senegal, Sao Tome & Principe, Togo Offset UTC 0:00 hoursĦ:30 pm 18:30 India Standard Time (IST). Greenwich Mean Time is 5 hours and 30 minutes behind India Standard Timeġ:00 pm 13:00 in GMT is 6:30 pm 18:30 in ISTīest time for a conference call or a meeting is between 8am-12:30pm in GMT which corresponds to 1:30pm-6pm in ISTġ:00 pm 13:00 Greenwich Mean Time (GMT).

What time zone am i in gmt