Author: Maxima ass
Date: 2020-03-11
Recently solve several problems related to time, a great harvest. Sudden and devastating finishing an article on time-dependent.
This paper describes the time-related concepts. The goal is: What GMT time to figure out? What is UTC time? They are our most popular Beijing and what is the relationship? And what is daylight saving time? It daily life, what impact? . After reading this article I want to be able to easily answer these questions.
One, GMT
GMT 's full name is: Greenwich Mean Time or GMT (Greenwich Mean Time) , the concept of the time the system established in 1884, is calculated from the Greenwich Royal Observatory in London and maintenance, and in the coming For decades diffusion to other European countries. From the beginning of 1924, the Greenwich Observatory every hour will be broadcast time to the world.
In the decades beginning, GMT measuring method is very simple: the observer always monitor the position of the sun in the sky, and the day when the sun climb to the highest elevation recorded this point in time is called "transit through" . 24 hours a day for the average person to understand, it is equivalent to roughly twice the Sun's transit through the interval. However, because the Earth's orbit around the sun is elliptical, the rate of travel on a different track, resulting in a year there will be "a long day" and "short day", so observers must Greenwich continuous observation of at least one year, and then take varying lengths 365, "day", then the average of all of them, one day to give a fixed length, then subdivided into time, minute and second units. This is GMT .
Two, UT
In recent decades, thanks to a more stable solar day observation method using the same universe stable periodic signal source of radio waves, with the angle of observation when the source wave reaches Earth directly calculate the rate of rotation and revolution of the earth, and then this calculation a year, one day, the average length of time every minute. These observations may be referred to other more high-tech observatory, or a satellite to be responsible for, and nothing to do with observing the Greenwich Observatory, so it has a new name: world (Universal Time) , the abbreviation UT .
There are three versions of the world, were called UT0, UT1 UT2 with
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UT0 observation is the most primitive Calcd
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UT1 is amended influence the Earth's axis of rotation at longer time scales will produce drift
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UT2 is to research needs, and more than UT1 corrected seasonal influence.
Thanks to UT, GMT should be fair to say that we should retire, but in fact due GMT name has been used for decades, but with the concept GMT UT1 to be measured is basically the same, are "long scale down the average solar day " , so the name was retained GMT.
Brief summary : GMT is antique, UT1 link between the past, but the general concept GMT = UT1, the mean solar day is observed, the use of two terms can be interchangeable.
Three, UTC
On the other hand, since the 1967 General Conference on Weights and Measures The second definition read: cesium atomic time after a fixed number of shocks, the measurement time can be out of touch with the planet's rotation. When using only atomic clock computing system time and date, known as the International Atomic (International Atomic Time), the time to International Atomic accounting basis, the time format and UT1 aligned, so that ordinary people have a convenient time used by the system is called Coordinated Universal Time (Universal Time Coordinated) , which is UTC . That is why UTC and GMT is almost the same.
Under the existing international system of units, the 13th International Conference of Weights and Measures in 1967 definition of "seconds": Cesium 133 atomic ground state of two ultra-fine energy level between transition 9,192,631,770 times the period of the radiated electromagnetic waves time
Because UTC is directly linked to the international standard of weights and measures, so that almost all international communications systems, such as satellites, aircraft, GPS and so on, all protocol uses UTC time.
Fourth, differences and connections
However, due to the Earth's rotation is slowly decelerating , resulting in an average solar day will gradually become longer. In other words, GMT will be one second longer and longer, but as long as we do not change the definition of weights and measures for the second, then the second will consistently UTC. Over time, UTC will be more than one second ahead of GMT, and will be more and more!
Therefore, it is responsible for the management of UTC dedicated agency decisions when one second faster UTC ahead of GMT, select the appropriate time adding leap seconds (can be compared in the lunar leap month ), to offset the advance amount.
Brief summary : GMT, U1 UTC and there is no difference in the case of general use, namely: GMT = U1 = UTC
Strict point : UTC using atomic timekeeping become the common standard international communications. UTC efforts to comply with the format and timing of the concept of GMT, so although not a big change, but every three to five years is necessary to add a leap second to wait GMT second.
Therefore GMT, U1, and UTC time for the average user is the same in magnitude, it does not need to strictly distinguished. The frequency of use in daily life GMT and UTC will be higher, but both represent the same concept.
Five time zones
If the timing of different ways (GMT, U1 and UTC) has little effect on people's lives, but it is closely related to the time zone and people's lives.
First, we need to figure out, what is the time zone? Why time zones?
In order to take into account ease of use in all regions, but also the rest of the people will easily convert local time to time to go somewhere else . International meeting decided according warp surface of the earth from east to west, into a designated regions.
Today the world is divided into 24 time zones. In fact, often a country or a province simultaneously astride two or more time zones, in order to take care of administrative convenience, often will draw together a country or a province. Therefore, the time zone is not strictly linear north-south divide, but by natural conditions to divide. For example, China covers a broad, almost across five time zones, but for ease of use simple, in fact, when only standard Timezone 8, namely Beijing time.
Put simply divide the time zone is to allow global communication more convenient (eg after, with the time zone, we can clearly know 6:00 is probably when the sun rises, the sun sets and 18:00 is probably the time)
for example:
Now if Z Zhang in Beijing, and his girlfriend little C in New York, if not divided area (if now 20:00), and that their time is the same (both 20:00). Zhang Z local time the sun goes down is just two hours, the little C local time What time is it? Morning or night? Now call is appropriate?
If you do not know this information it will bring a lot of inconvenience to communicate.
But if the division of time zones , we know that if 20:00 Beijing (East eight districts) time (GMT + 8), happens to be in New York 7:00 (West Fifth District) time (GMT-5). So Zhang Z at 20:00 when he knows now there is a small C 7:00 in the morning, according to the normal schedule, girlfriend may still rest, is not convenient to call.
Time zone calculation
= Calculated time zone zone known - (time zone of known area - to calculate a time zone region). (Note: Eastern time zone is positive, the West time zone is negative)
The following example will be described:
Example 1: Known Tokyo (Kowloon East district) time at 12:00 on May 1, when (East eight districts) District Beijing seeking.
Beijing Time = 12: 00 (9-8) = 11:00, Beijing time is at 11:00 on May 1.
Example 2: Given Beijing at 12:00 on May 1, when demand (time zone) of Canary Wharf.
London time = 12: 00 (8-0) = 4:00, that is London time at 4:00 on May 1.
It is known that Beijing at 12:00 on May 1, find New York (West Fifth District) District: Example 3.
New York time = 12: 00- [8 - (- 5)] = - 1: L00 + 24: 00-1 = 23 days: 00 New York i.e. time of 23:00 on April 30. (Note: When the calculated negative zone, should be added to 24:00, date minus one day, i.e. changed from May 1st April 30)
Local time = GMT + :( local time zone time difference)
:( GMT GMT = GMT + 8)
Sixth, daylight saving time
Summer Time, also known as daylight saving time, daylight saving time (English: Daylight saving time), is an energy-saving system to prescribe the place and time, unified time during the implementation of the system used is called "Daylight Saving Time time". In general man-dawn early summer time by one hour from, can make early bed early, reducing the amount of illumination, in order to make full use of light resources, thereby saving lighting.
For example, C small place where the winter sun rose at seven o'clock, seven o'clock every morning to get her day studying twelve hours in the study, seven pm to sleep. By the summer sun becomes a six-point rise, now six o'clock at first light, if at this time a small C or seven o'clock to get up, then the equivalent of 'waste' for an hour photoperiod. And if the time on the alarm clock set forward one hour (an hour before the sun rises up), then the same get up at seven (shown on the alarm clock is actually six and seven), learning twelve hours, to six o'clock in the evening to go to bed (saving electricity time of 6 to 7). Therefore, the use of regional summer time, advocate early hours equivalent, so that the residents can enjoy the natural sun off as much as possible, so as to achieve the purpose of saving household electricity.
Zhang Z or borrow example:
If this were 2020, March 11, as New York has implemented daylight saving time, so the local time will be advanced one hour. This means that if Zhang was in Beijing 20:00 Z wanted to call his girlfriend, then due to Daylight Savings Time, 8:00 am New York time already (Note: GMT time is the same, just change the local time) , according to the normal schedule, the small C should have to get up now easy call. So because of daylight saving time, Zhang Z an hour early to contact his girlfriend.
Therefore, when considering local daylight saving time, its formula should be:
Local time = GMT + :( local time when daylight saving time zone differences +)
Note: When China currently does not observe daylight saving time (in fact, just modify working hours and rest most of the company's so-called daylight saving time, does not modify local time)
Eight Review
So far, the concept of time on introductions, and look at our goal: to figure out what GMT time? What is UTC time? They are our most popular Beijing and what is the relationship? And what is daylight saving time? It daily life, what impact?
Now you understand it? If any part is not clear, please look again.
Nine, reference links
(Finish)