What is GMT? What time is it? How to calculate the time from Greenwich

Until now, in the computer settings of Windows, the time zone is set with the abbreviation GMT. What is this and how does it relate to the modern UTC time coordination system? We will discuss this in our article. Not everyone can determine the time at the point of location relative to Greenwich. But we will try to clarify this question in a popular language. First of all, you need to answer the question: "What is GMT?" How does this abbreviation stand?

British Snobbery

In the olden times, it was set at noon. When the sun was at its zenith, that is, reached its highest point in the visible sky, it was believed that it was twelve o'clock in the afternoon. With the development of international trade, it became necessary to coordinate time in a single system. The point of such a reference was the zero meridian. It passes through the Royal Observatory in Greenwich, near London.

Thus, the abbreviation GMT stands for Greenwich Mean Time. All the territories that are to the west of Greenwich are lagging behind its time, and those that are located to the east are ahead of it. There is another significant meridian on the surface of the planet Earth. This is the line for changing dates. The territory, located to the east of it, lives (in the literal sense of the word) yesterday. In 1972, the new abbreviation UTC replaced GMT. What is this time? The abbreviation stands for "Universal Coordinated Time".

Time Zones

The Russian-speaking metrology uses the abbreviation SGV instead of GMT. What is that? The letters "Middle geographic time" are deciphered. But again, from Greenwich, we can not escape. After all, the whole world counts the clock from the zero meridian. If to be punctual and precisely determine the time for each point on the globe, you need to know its distance from Greenwich to the west or east. A Coordinated Universal Time (in other words UTC) displays mostly noon in certain countries (or parts of them). If GMT is time that does not know political boundaries, then time zones often spread to the whole state (if it does not extend very far from west to east). Thus, UTC + 0 is not time at the Greenwich Observatory and the zero meridian, but in the whole of Great Britain and Ireland, as well as Iceland, Portugal, Morocco, etc. But the clock is calculated according to the TCB system in the same way as In GMT.

Summer and winter time

In countries lying in high latitudes, the duration of a day of light varies greatly depending on the season. Therefore, northern countries often switch to summer time. The inhabitants of these states shift the hands of the clock for an hour ahead. This happens on the last Sunday in March. The UK is also on the list of countries practicing the summer period of the clock. But the true noon from April to October is observed then at one o'clock in the afternoon, because the average time in Greenwich does not depend on the season.

Countries lying near the equator, where the duration of a light day at any time of the year is approximately twelve hours, do not shift seasonally the arrows. They live constantly in winter (true) time. On this basis, the Russian Federation decided not to move the arrows an hour ahead. By the way, another country, lying in high latitudes, refused to switch to summer time. This is Iceland. The island state lives in the Middle Greenwich time (GMT + 0). Lying approximately on the same meridian, Great Britain and Ireland in winter are in UTC + 0, and in summer - in UTC + 1.

What is UTC and GMT for?

Time is a concept that loves accuracy. For coordinated actions to dispatching services located at remote points of the Earth, it is necessary to know how many hours, minutes and seconds there are. Also the need for a coordinated time has also broadcasters of different frequencies. UTC is necessary to establish a certain standard for navigation and scientific purposes. Throughout the nineteenth century, the sailors of the British Navy, the furrow of the World Ocean, calculated the time by GMT. Moving west of Greenwich, they took hours, and to the east - pushed. By this principle, the globe is now divided into temporary belts. For example, Vladivostok time corresponds to GMT + 11, Georgian - GMT + 4, Hawaii-Aleut - GMT-10, Moscow - GMT + 4, Standard Eastern Time (it is used for New York and adjacent to the Atlantic Ocean territories of the USA and Canada, and Also in Jamaica, Panama, Haiti, the Bahamas) - GMT-5.