About GMT and UTC (GO)

Source: Internet
Author: User
Tags time zones local time

About GMT and UTC

First, Introduction

Many people know that the two-way schedule is referred to as GMT or UTC, and the World Time Zone table is referred to as universal, so what is the actual intent of GMT and UTC? How is the world time zone differentiated? What is the meaning and function of the dense English words on the face plate? These are the questions that come to mind as novices approach the two-place timetable or the World time zone table, and the following will take you through the wonders of the time zone.

Ii. Sources of history

1) Greenwich Mean time GMT

In the seventeenth century, the Royal Observatory of Greenwich conducted celestial observations for the expansion of maritime hegemony. In 1675, the Old Royal Observatory was formally established. In 1884, it was decided to use the meridian of Greenwich as the longitude of the earth and the two hemispheres. There is a 24-hour clock on the wall of the Observatory, showing the current time. For the world, the time set here is the World Time Reference Point. The time is set globally with Greenwich Mean Time as the standard. This is the origin of our familiar Greenwich Mean Time (GMT). When it is marked on the watch, it means that the watch has two time functions, that is, it can display both the original place and another country. time.

2) World Coordination time UTC

Most of the timetables in the two places are expressed in terms of GMT, but there are also some GMT words on the timetables of the two places. What is happening is the three English letters UTC. What is UTC? In fact, UTC refers to Coordinated Universal Time (also known as World Standard Time, World Uniform Time), which is the new time scale after the correction of the Earth's axis motion after the average solar time (based on GMT of Greenwich Mean Time). As well as the time calculated by the international atomic time in "seconds", the calculation process is quite rigorous and precise. Therefore, UTC is more accurate than GMT in terms of "world standard time". The error value must be kept within 0.9 seconds. If it is greater than 0.9 seconds, the leap second is issued by the Central Bureau of International Earth Rotation in Paris, which makes UTC consistent with the Earth's rotation period. So basically the essence of UTC emphasizes a more accurate world time standard than GMT, but for the current model, there is no difference in the function and accuracy of GMT and UTC.

3) Summer Time saving DST

When it comes to the Date class in java.util, we often refer to UTC and GMT, which are almost the same concept. They all refer to Greenwich Mean Time, but UTC's name is more formal. The difference between the two is that the former is an astronomical concept, while the latter is based on an atomic clock. In UTC, there is a "leap second" every year or two.

UTC and GMT time each region has its own local time, the problem of time conversion in the Internet and radio communication is particularly prominent. I have often confused myself with this, specially researched, records here for forgetting.

The entire Earth is divided into 24 time zones, each with its own local time. In international radiocommunication situations, for the sake of unification, a uniform time is used, known as universal Coordination (UTC, Universal-time coordinated). UTC, like Greenwich Mean Time (GMT, Greenwich Mean time), is the same as in London, England. In this article, UTC and GMT mean exactly the same.

Beijing time Zone is East eight, leading UTC eight hours, in the date field of the e-mail letterhead is recorded as +0800. If you have such a line in the letterhead of an e-mail message:

DATE:FRI, Geneva 2002 09:42:22 +0800

The place where the letter was sent is November 8, 2002, Friday, 9:42 A.M. (22 seconds), and the local time of this place is eight hours ahead of UTC (+0800, which is the East eight zone time). The date field of the e-mail letterhead uses a 24-hour clock instead of the AM and PM to mark the afternoon.

Take the sending time of this email as an example, if you want to convert this time to UTC, you can use the formula:

UTC + time Zone difference = local time

The time zone Chadong is positive and the West is negative. Here, the East eight zone time difference is recorded as +0800,

UTC + (+0800) = local (Beijing) time (1)

So, UTC = local time (Beijing time))-0800 (2)

0942-0800 = 0142

That is, UTC is 1:42 A.M. 22 seconds on that day. If the result is negative, it means the day before UTC, and the negative number plus 2400 is UTC at the previous time. For example, local (Beijing) time is 0432 (4:32 A.M.), then UTC is 0432-0800 =-0368, minus sign means the day before,-0368 + 2400 = 2032, both the night before 8:32.

New York's time zone is West Five, which is five hours behind UTC and is recorded as-0500:

UTC + (-0500) = New York Time (3)

UTC = New York Time + 0500 (4)

Comparing (2)-(4)-type,

UTC = Beijing Time-0800 = New York time + 0500 (5)

GMT = New York Time + 1300 (6)

That is, Beijing time 13 hours ahead of New York, by the (6) type,

New York time = Beijing Time-1300 (7)

In late April, New York switched to daylight saving time, also known as daylight savings, one hours earlier than standard New York, and actually became the standard time for the West quarter, becoming-0400.

UTC + (-0400) = New York Daylight Time, apply the above formula,

BEIJING time = New York Daylight + 1200

New York Daylight Time = Beijing Times-1200

In these transformations, the most important formula is

UTC + time Zone difference = local time

The time zone Chadong is positive and the West is negative. For example, East Eight district (Beijing) is +0800, West Five district (New York) is-0500, California is the West eight district, is-0800, the central US time zone is the West six zone,-0600, the United States Mountain Time Zone is the West Seven district, 0700, the Pacific Time Zone is the West Eight district,-0800, in summer daylight saving Becomes-0700. The German time zone is the eastern one, +0100 and summer +0200.

Most e-mail programs, such as Outlook Express, display time when the computer program converts the time to a local time before displaying it, for example, the Date field of the message is:

DATE:FRI, Geneva 2002 09:42:22 +0800

Outlook Express appears when it is displayed as:

Date:thur, 2002 08:42:22 pm, converted the time of Beijing to New York time and converted the 24-hour format into a 12-hour format. Of course, for the time conversion is correct, the sender and receiver of the computer's time zone should be set correctly, here, the sender's time zone is correctly set to the Beijing time zone East eight, and my time zone is set to the West five zone.

For the sake of convenience, I'm here to put the clocks in New York, California and Beijing in real time to save the hassle of computing.

About GMT and UTC (GO)

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