Time zones, GMT, UTC, CDT. GMT - what is this time? How to calculate time from Greenwich

So far in computers Windows settings the time zone is given by the abbreviation GMT. What is it and how does it relate to modern system coordinating UTC time? We will talk about this in our article. at the point of location relative to Greenwich, not everyone can. But we will try to explain this question in popular language. First of all, you need to answer the question: "GMT - what is it?" How is this abbreviation deciphered?

British snobbery

In the old days, the time was set at noon. When the sun was at its zenith, that is, it reached its highest point in the visible sky, it was believed that this was twelve o'clock in the afternoon. With the development of international trade, it became necessary to coordinate the time in single system. The point of such a reference was He passes through the Royal Observatory in the town of Greenwich, not far from London.

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

Time Zones

In Russian metrology, the abbreviation SGV is used instead of GMT. What is it? The letters are deciphered as "Geographical Mean Time". But again, we can't get away from Greenwich. After all, the whole world is counting hours from the prime meridian. If you are punctual and accurately determine the time for each point on the globe, you need to know its distance from Greenwich to the west or east. And Coordinated Universal Time (in other words UTC) displays basically noon in certain countries (or parts of them). If GMT is a time that knows no political boundaries, then time zones often extend to an entire state (if it does not extend very much from west to east). Thus, UTC + 0 is the time not in and on the zero meridian, but in the whole of Great Britain and Ireland, as well as Iceland, Portugal, Morocco, etc. But the calculation of hours using the UTS system is carried out according to the same principle as in GMT .

Summer and winter time

In countries at high latitudes, the length of daylight hours varies greatly depending on the time of year. Therefore, northern countries often switch to daylight saving time. Residents of these states move the clock forward one hour. It takes place on the last Sunday in March. The UK is also on the list of countries that practice the summer clock period. But true noon from April to October is then observed at one o'clock in the afternoon, because Greenwich Mean Time does not depend on the season.

Countries lying near the equator, where at any time of the year is approximately equal to twelve hours, do not shift the hands seasonally. They constantly live in winter (true) time. On this basis and the Russian Federation I decided not to move the hands forward an hour every year. By the way, another country lying in high latitudes refused to switch to daylight saving time. This is Iceland. The island nation lives on Greenwich Mean Time (GMT+0). Lying approximately on the same meridian, Great Britain and Ireland are in UTC + 0 in winter, and in UTC + 1 in summer.

What are UTC and GMT for?

Time is a concept that loves precision. For coordinated actions, dispatching services located in remote points of the Earth need to know what hours, minutes and seconds it is. Broadcasters of different frequencies also have a need for coordinated time. UTC is necessary to establish a certain standard for navigational and scientific purposes. Throughout the nineteenth century, sailors of the British Navy, sailing the oceans, calculated the time according to GMT. Moving west of Greenwich, they took away hours, and east they added. According to this principle, it is now divided into time zones. For example, Vladivostok time corresponds to GMT + 11, Georgian time corresponds to GMT + 4, Hawaiian-Aleutian time corresponds to GMT-10, Moscow time corresponds to GMT + 4, Eastern Standard Time (it is used for New York and the territories adjacent to the Atlantic Ocean of the USA and Canada, and also in Jamaica, Panama, Haiti, Bahamas) - GMT-5.

Instruction

Determine the offset of your time zone from the Greenwich meridian. You can find it out, for example, from the system time settings in your operating system. Click the clock in the notification area of ​​the taskbar with the left mouse button, and an additional panel with a calendar and analog clock will pop up on the screen. At the bottom of it is a link "Change date and time settings" - click on it. The system will open an additional settings window with three tabs, one of which is "Date" and has a "Time zone" section. In this section, you will see the shift of your local time relative to the Greenwich meridian - the corresponding inscription may be, for example, this: "UTC +04:00 Volgograd, Moscow, St. Petersburg." It's that time of your system clock operating system shifted four hours ahead of the zero time zone.

Subtract the time offset set for your time zone from the current time in order to determine the corresponding GMT time. For example, if your clock shows 26 minutes past 9 a.m. and the time zone matches the time, then this offset is four hours, and you are now 26 minutes past five in GMT.

Use the Greenwich Mean Time service if you have Internet access. This is an even easier way. For example, you can follow the link http://time100.ru/gmt.html and you will see the current GMT time immediately, without additional calculations.

Use the built-in functions of the programming language if you need to determine Greenwich Mean Time programmatically- they are provided in most scripting languages. More often, such functions refer to UTC time, and this is reflected in their names. For example, in PHP these are the gmdate and gmmktime functions, in JavaScript it is an entire set of functions (getUTCDate, getUTCDay, getUTCMilliseconds and others), in MQL5 it is TimeGMT, etc.

Sources:

• GMT

Due to the fact that the size of our planet is huge, in the same period of time, at different points on the Earth - their own local solar time. And in order to avoid confusion in clarifying the question: “So what time is it?”, A standard time system was adopted. And the Earth was conditionally divided into 24 sentries belts. The zero meridian was taken as a starting point, from which they go east sentries belts+1, +2, +3, etc., and to the west: -1, -2, -3, etc. So, thanks to the time zone system, it is now quite easy to determine what you are looking for.

You will need

• - computer
• - map of time zones
• - world map showing degrees of longitude

Instruction

Turn on and click on the clock indicator in the lower right corner of the screen. Now, in the window that opens, click on the "Change date and time settings" function. And, already in the new window, select the "Change time zone" function. You will see a long list of cities that belong to them. Of course, only the capitals are listed here and there are no small towns. So, if you want to know the time zone of a small city, just find the capital of its country in this list, because, usually, one time zone operates within one country.

Use an ordinary map of the world, which shows in detail the average meridians: 0°, 15°, 30°, 45°, 60°, etc. The fact is that one time zone takes approximately 15 °, but not clearly from 0 ° to 15 °, from 15 ° to 30 °, from 30 ° to 45 °, etc., but with an offset that is equal to - 7 °30. A , in order to define the boundaries, for example, of a sentry belts UTC + 1, it is necessary to draw to the right and left of the middle meridian 15 ° east longitude at a distance of 7 ° 30 ". In order to determine the time zone of a place that is located, for example, in the region of 60 ° west longitude, it is necessary to calculate its position according to in relation to the prime meridian: 15° - one, 30° - two, 45° - three, 60° - four.So 60° west longitude is the UTC-1 time zone.

Use the detailed map of time zones. This is the simplest and reliable way determine the time zone of a particular point on the globe. Since here, not only the boundaries of each of the 24 time zones are indicated, but there is also a note - whether it goes over to time. It looks, for example, like this: +1(+2), and that the country belongs to the UTC + 1 time zone, but in the summer, it belongs to the UTC + 2 time zone. Of course, do not forget to take into account that in different hemispheres summer and winter at different times. Another big plus of such a map is the ability to determine whether different sentries belts, as in Russia, or, despite the large territory, only one belt is accepted, as in China.

note

Despite the generally accepted system of time zones, in reality, in order to maintain a single time within one country or administrative unit, the boundaries of the zones are shifting, so in some places some time zones are crowded out by neighboring ones.

Useful advice

When determining the time zone, keep in mind that in some countries, local time differs from universal time not only by a standard hour, but also by an additional 30 or 45 minutes.

When trying to find out how many in another region and in another country, you will most likely come across the concept of " hourly belt". But often it is denoted by a special abbreviation GMT. Where did she come from, and what does she mean?

GMT is the English phrase Greenwich Mean Time, which is like "Greenwich Mean Time". The mean time is understood as the astronomical time of the meridian, on which the Greenwich Observatory was previously located. This place is considered the "reference point" for all sentries belt ov.Greenwich Royal Observatory has become a place of reference for a reason. It appeared in the 17th century in Greenwich (England). There were important calculations for navigators, including those relating to time. When Great Britain became the largest empire, the GMT time calculation spread to dependent states, and at the end of the 19th century, almost the whole world adopted this reporting system. In 1884, even a special international conference was held to determine the "reference meridian". Time in other countries was determined by the distance from the Greenwich meridian, that is, from that hour belt and where Great Britain was located. In the seventies, the time reference system was replaced by a more accurate one - by calculation according to universal coordinated time, which is slightly different from the time on the Greenwich meridian. Nevertheless, the abbreviation GMT is still often used as a tribute to tradition. What do the numbers before the abbreviation GMT mean? This is in the Greenwich Observatory and other selected area. For example, if you are in a sentry belt e GMT + 3, for example, in Moscow, the time difference with the reference meridian is three hours, while in Moscow the time is later. The minus sign in front of the number indicates that the time must be counted in the opposite direction: when it is 11 o'clock in London, then it is 9 more in the region with GMT-2. But at the same time, one should not forget that not all countries have hours for winter time. In 2011, it was also canceled in Russia. In this case, the GMT indicator will change depending on the season.

The appearance of the time zones of our planet was due to the banal convenience of communication and separation different countries and cities according to real time days. Scientists have divided the entire surface of the Earth into 24 time zones, while taking into account a gap of 15 degrees of longitude. The same time is considered to be within the same time zone.

Instruction

The decision to calculate time zones was made at International Conference in 1884. The meridian passing through the Greenwich Observatory near London began to be considered a year as a time reference point. It was this observatory that became the unifying link. Initially, it was built by order of King Charles II for sailors.

Instant.now() // Capture the current moment in UTC.

Generate a string to represent this value:

Instant.now().toString()

2016-09-13T23:30:52.123Z

details

In Java 8, the current moment is only captured with a resolution of up to milliseconds. Java 9 has a fresh Clock implementation that captures the current moment up to the full nanosecond capability of this class, depending on the capabilities of your host computer's clock hardware.

Its toString method generates a string representation of its value using one specific ISO 8601 format. This format outputs zero, three, six, or nine digits (milliseconds, microseconds, or nanoseconds) as needed to represent a fraction of a second.

If you want more flexible formatting or other additional functions, then apply a zero offset from UTC to UTC itself (ZoneOffset.UTC constant) to get OffsetDateTime .

OffsetDateTime now = OffsetDateTime.now(ZoneOffset.UTC);

Dump to console...

System.out.println("now: " + now);

When you run...

Now: 2014-01-21T23:42:03.522Z

DateTimeZone zoneMontréal = DateTimeZone.forID("America/Montreal"); DateTime now = DateTime.now(zoneMontréal); DateTime now = DateTime.now(DateTimeZone.UTC);

If you really want to use the JVM's current timezone by default, make an explicit call so that your code is self-documenting.

DateTimeZone zoneDefault = DateTimeZone.getDefault();

Standard time - a system of counting hourly time, based on the division of the Earth's surface into 24 time zones, every 15 ° in longitude. Time within the same time zone is considered the same. In 1884, at the International Conference, it was decided to apply this system. In accordance with the international agreement of 1883, the initial ("zero") meridian is the one that passes through the Greenwich Observatory in the suburbs of London. Local Greenwich time (GMT), agreed to be called universal or "World time"

On the territory of Russia, since March 28, 2010 - 9 time zones (before that there were 11 time zones). Samara region and Udmurtia switched to Moscow time (second time zone). Kemerovo region. (Kuzbass) - to Omsk (MCK+3). Kamchatka Territory and Chukotka - to Magadan (MSK + 8). In these five subjects of the Federation, March 28, 2010 - the clock hands were not translated.

Two belts are abolished - the third (Samara, MSK + 1) and the eleventh (Kamchatsky, MSK + 9). There are 9 of them in total, and the maximum time spread in our country is reduced from 10 to 9 hours.

In Russia, since March 2011, after the transition to summer time, the clock hands are no longer translated during the year.

In 2012 - again discussed, at all levels, the advantages of a permanent winter time over summer time, therefore - a transition (this autumn) to a permanent, year-round winter time is possible.

Stable time is better for health. In the autumn-spring off-season, the body will not have to especially rebuild its biorhythms. Technical Services and transport workers now do not have to, as before, when translating the hands of the clock, reconfigure equipment and change schedules.

Moscow time zone, stable time: +4 (GMT + 4:00)

Standard time boundaries are drawn taking into account physical and geographical features - along large rivers, watersheds, as well as along interstate and administrative borders. States can change these boundaries within the country.

The international system U T C (World Time; it is designated UTC / GMT or, which is the same - UTC), as well as the difference between local and Moscow time - MSK is used. The plus sign means - to the east, "minus" - to the west of the starting point

The transition to summer time (one hour ahead) and winter time (one hour ago) is carried out in spring and autumn, respectively. This rule is valid in the European Union, Egypt, Turkey, New Zealand... Dates and order of transfer - may slightly differ in terms. Most countries have abandoned the autumn-spring shift of the clock: Russia and Belarus (since 2011), Kazakhstan, Turkmenistan, Uzbekistan, Tajikistan, India, China, Japan, Singapore, Taiwan ...

World time - UTC/GMT - the value of Greenwich Mean Time (G M T) is equal to "Universal Coordinated Time" (U T C) with an accuracy of one second - GMT=UTC). The name U T C will, over time, completely replace the term "Greenwich time"

Rice. 2 Map - World time zones and their offsets from UTC / GMT (Greenwich Mean Time)

Table - time zones of world cities (UTC / GMT), in the summer

Kamchatka	UTC/GMT+12
Magadan, Sakhalin.	UTC/GMT+12
Vladivostok	UTC/GMT+11
Yakutsk	UTC/GMT+10
Irkutsk	UTC/GMT+9
Krasnoyarsk	UTC/GMT+8
Omsk	UTC/GMT+7
Yekaterinburg	UTC/GMT+6
Moscow Moscow time, city of Sochi	UTC/GMT+4
Minsk "Eastern European Time" (EET)	UTC/GMT+3
Paris "Central European (Central European) Summer Time" (CEST - Central Europe Summer Time Zone)	UTC/GMT+2
London "Greenwich Time" / "Western European Time" (WET)	UTC/GMT+1
"Mid-Atlantic Time"	UTC/GMT-1
Argentina, Buenos Aires	UTC/GMT-2
Canada "Atlantic Time"	UTC/GMT-3
US - New York "Eastern Time" (EDT - US Eastern Daylight Time Zone)	UTC/GMT-4
Chicago (Chicago) "Central Time" (CDT - US Central Daylight Time)	UTC/GMT-5
Denver "Mountain Time" (MDT - US Mountain Daylight Time)	UTC/GMT-6
USA, Los Angeles, San Francisco "Pacific Time" (PDT - Pacific Daylight Time)	UTC/GMT-7

An example of the designation of winter and summer time: EST / EDT (Eastern Standard / Daylight Time Zone).
If, somewhere, winter time is considered standard, then it can be abbreviated, for example: ET, CT, MT, PT

Table - time zones of cities and regions in Russia, since 2011.
The local time difference is shown:
MSK + 3 - with Moscow;
UTC+7 - with Coordinated Universal Time (UTC = GMT)

Name winter / summer		Bias relatively Moscow time	Offset from UTC (world time)
USZ1	Kaliningrad time - the first time zone	MSK-1	UTC+3:00
MSK/MSD MSST/MSDT	Moscow time	MSK	UTC+4:00
SAMT/SAMST	Samara	MSK	UTC+H:00
YEKT / YEKST	Yekaterinburg time	MSK+2	UTC+6:00
OMST/OMST	Omsk time	MSK+3	UTC+7:00
NOVT/NOVST	Novosibirsk, Novokuznetsk Kemerovo, Tomsk. Barnaul	MSK+3	UTC+7:00
KRAT / KRAST	Krasnoyarsk time Krasnoyarsk, Norilsk	MSC+4	UTC+8:00
IRKT / IRKST	Irkutsk time	MSK+5	UTC+9:00
YAKT / YAKST	Yakut time	MSK+6	UTC+10:00
VLAT/VLAST	Vladivostok time	MSK+7	UTC+11:00
MAGT / MAGST	Magadan time Magadan	MSK+8	UTC+12:00
PETT / PETST	Petropavlovsk-Kamchatsky	MSK+8	UTC+I2:00

Note: MSK = MSD (Moscow Summer Time) throughout the year

Terms and Definitions

Switching to Daylight Saving Time (DST - Daylight Saving (Summer) Time) - moving the clock forward one hour, which was carried out annually on the last Sunday of March, in order to get an extra hour during daylight hours, to save electricity (for lighting, etc. ). The return to winter time was carried out in the last. Sunday October. These transitions affected the biorhythms of the human body, his well-being, and it took a week of adaptation to get used to. Manipulation of the hands of the clock - common cause lateness of workers and employees to work.

The initial (zero) meridian - the Greenwich meridian with geographical longitude equal to 0°00"00", divides the globe into the western and eastern hemispheres. Passes through the former Greenwich Observatory (in the suburbs of London)

GMT (Greenwich Mean Time) - "Greenwich Mean Time" on the Greenwich meridian. It is determined by astronomical observations of the daily movement of stars. It is unstable (within a second per year) and depends on the constant change in the speed of the Earth's rotation, the movement of the geographic poles on its surface and the nutation of the planet's axis of rotation. Greenwich (astronomical) time is close in value to UTC (atomic time), and for the time being will be used as its synonym. Also called "Zulu Time"

In Russian-speaking meteorology, GMT is denoted as GMT (Greenwich Mean / or Geographic / Time)

GMT= UTC (accurate to 1 second)

Time zone (Standard time zone) - difference from UTC / GMT World Time (example: UTC / GMT + 4 - the fourth time zone, east of Greenwich)

H:mm:ss - 24 hour format (example: 14:25:05). Minutes and seconds - with leading zeros

h:mm:ss - 12-hour format (example: 02:25:05 PM - "two and a half hours in the afternoon" - 14:25:05). Minutes and seconds - with leading zeros

AM - designation of time before noon in 12-hour format (abbreviated version - "A")
PM - designation of the time after noon in 12-hour format

Universal Time UT (Universal Time - Universal Time) - the mean solar time on the Greenwich meridian, is determined by astronomical observations of the daily movements of stars. Its updated values ​​are UT0, UT1, UT2

UT0 - time on the instantaneous Greenwich meridian, determined by the instantaneous position of the Earth's poles

UT1 - time on the Greenwich mean meridian, corrected for the movement of the earth's poles

UT2 - time, taking into account changes in the speed of rotation of the Earth

TAI - atomic clock time (International Atomic Time, since 1972). Stable, reference, never translated. Time and frequency standard

Time in the system GPS navigation has been operating since January 1980. It does not include amendments. It is ahead of the UTC time by 15 seconds.

UTC (from English Universal Time Coordinated)- Coordinated Universal Time for the coordinated distribution of standard frequencies and accurate time signals on radio, television and the Internet - "World Time". Its synonym is "Universal Time Zone"

The UTC time scale has been introduced since 1964 to harmonize UT1 (astronomical measurements) and TAI (atomic clocks).

Unlike GMT, UTC is set using atomic clocks.

The speed of rotation of the earth is slowing down, in connection with which corrections are regularly introduced into the UTC scale, after a year or two or three, on June 30 or December 31 (leap seconds - "Second of coordination"), so that UTC is not more than a second ( more precisely - 0.9 s) differed from astronomical time (determined by the movement of the Sun), as UT1 lagged behind by a second. This international rule was adopted in 1972.

The ratio of time in 2009: UTC (universal) lags behind TAI (atomic) - by 35s. Time in the GPS navigation system - ahead of UTC by 15 seconds (the countdown is from 1980, the difference is increasing) T glonass = Tutc + 3 hours (adjusted, so the discrepancy between them does not exceed 1 ms.)

Precise time signals (for clock synchronization) are transmitted via radio channels, television, the Internet - in the UTC system. More precisely, you can put, for example, on the signal of the Mayak radio, but only on the long-wave or medium-wave range (on the "earth-surface wave"). On the VHF / FM radio band, the signal may be delayed up to several seconds from the true one.

In watches with automatic synchronization (eng. Radio controlled), time correction occurs from base stations, on ultra-long waves. This system has been developed in Europe.

Numbers of exact local time services in Russian cities 100 - Moscow Voronezh Cheboksary Chelyabinsk 060 - Bryansk Kaliningrad Krasnodar Murmansk St. Petersburg Samara U mobile operators similar service no, because the mobile phone is not limited geographically and can work not only in a certain city, but also in roaming.

UTC time is not translated in winter or summer, therefore, for those places where there is a transfer to summer time, the offset relative to UTC changes (in Moscow, before the abolition of winter time in 2011, the difference was: in winter - UTC + 3, in summer - UTC+4).

Standard abbreviations for the names of calendar months and days of the week in English (used in RSS and others): January February March April May June July August September October November December Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Monday Tuesday Wednesday Thursday Friday Saturday Sunday Mon Tue Wed Thu Fri Sat Sun

GMT - Greenwich Mean Time (GMT) - the time of the meridian passing through the old Greenwich Observatory near London. It is used as a designation of time on weather charts. Synonyms for GMT are GMT and UTC.

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Literature

"Time and calendar" - M .: Nauka. 1989

Global (satellite) navigation systems GLONASS (Russia), GPS (USA), Galileo (European Union) - make it possible to determine, using navigators, including portable ones, the current location (coordinates), trajectory and speed of objects in any point of our planet and in near-Earth outer space.

According to the method of operation and purpose, satellite GPS (Global Positioning System) navigators are automobile (car navigators), portable, marine, etc. The most common imported ones are Garmin, Mio, etc. There are completely autonomous configuration options - with battery charging from solar panels or miniature thermoelectric generators (thermocouples). The navigation system is built into modern communicators, smartphones and Cell Phones, allowing you to receive not only geographical coordinates receiver location, but also the system time with an accuracy of fractions of a microsecond.

The Russian GLONASS (Glonass) has been operating since the mid-1990s. The orbital constellation includes more than two dozen active satellites. The system operates throughout Russia. Since 2009, transport, including passenger vehicles, has been massively equipped with this system.

Navigators are produced in Russia (Glospace SGK-70 and others) that can work simultaneously with several navigation systems- GLONASS, GPS, Galileo.

Glospace supports the SMILINK system (shows traffic jams) and is able to lay detour routes. Signals can be received from several satellite systems at once.

G P S maps - electronic maps for navigators and others mobile devices(communicators, pda / pda, smartphones, etc.) with GPS function.