Universal time and time zone division
Daniel J. Bufenstine once said, “Man’s first and greatest discovery is time.” Time is one of the most basic physical quantities, and the accuracy of contemporary time measurement has reached a very precise level.
Time is invisible, intangible, and its existence can only be perceived in motion.
Looking at the history of measuring time, we are constantly looking for periodic motion and using a fraction of the motion cycle as the basic unit of time measurement, one second.
The flow of shadows, dust, water, and the flow of the event itself are all transformed into the movement of time and become a faithful record of human activities on earth. Only clocks can mark the week, month, year, every second, every minute, every hour, and every day, thus liberating human beings from the monotonous cycle of nature.
Measurement of time
(1) Time
There is neither a starting point nor an ending point, and a straight line can be used to represent the time scale. Time has the property of no return and always flows in one direction, from the past without a source, through the present, and continuously flowing into the endless future.
(2) Measurement of time
Time can be measured, and various clocks are instruments for measuring time.
There are two types of measurement of time.
1. Time measurement
Measure an instant of time (a point on a time scale).
Time measurement requires a unit of measurement and a starting point for measurement. Midnight is the starting point for time measurement. For example, the train departure time is: 17:30, “hour” and “minute” are the units of measurement.
2. Period measurement
Measures the interval between 2 instants (two points on a time scale).
Period measurement only requires measurement units and does not require a measurement starting point. For example, the newly opened high-speed train from Beijing to Guangzhou only takes 8 hours from driving to arrival. “Hour” is the unit of measurement and has nothing to do with the starting point.
(3) Establishment of time benchmark
The basis for measuring time in ancient times relied on the movement of celestial bodies. The so-called “work begins at sunrise and rests at sunset.” Just as you need a ruler to measure length, you also need a benchmark to measure time. https://watcheshome.com/
1.True solar day
The period when the center of the sun passes through local noon twice in a row is called a day.
Due to changes in the distance between the earth’s orbit and the sun, the speed of the earth’s rotation also changes, so the length of each true solar day is different. The longest and shortest true solar day differ by dozens of minutes. Therefore, using the true solar day as the basis of time is inaccurate.
2.Mean solar day
The ancient Egyptians divided a day into 24 hours, an hour into 60 minutes, and a minute into 60 seconds
In 1820, French scientists held a meeting and decided to express the length of a day by the “average” of one year of the Earth’s rotation, which was recognized by the scientific community as the benchmark for time measurement. There are 86,400 mean solar seconds in a mean solar day.
3.Almanac seconds
In 1939, British scientist Jones discovered that the “Earth’s rotation” cycle changed significantly every year after long-term astronomical observations. He believed that the “mean solar day” time base established based on the Earth’s rotation was also unstable.
In 1956, scientists proposed establishing a new timing benchmark based on the “Earth’s revolution”. However, the Earth’s annual revolution period is also different, so the length of the solar return year at 12 noon on January 1, 1900 was used as the measurement benchmark. . This benchmark was obtained after years of research, and its accuracy has been greatly improved.
1/31556925.9747th of the time it takes for the Earth to orbit the sun once is regarded as one almanac second. The almanac second has been officially used since 1960.
4. Atomic second
With the advancement of science and technology, it was discovered that atoms have an extremely stable vibration frequency. In 1967, the 13th International Conference on Weights and Measures officially decided to replace the almanac second with the atomic second. The international standard second is obtained using an atomic clock, which is accurate to an error of 1 second per 3 million years.
Yan-133 When an atom transitions between two hyperfine energy levels in its ground state, it absorbs or radiates electromagnetic wave oscillation. The duration of 9192631770 cycles is one second of the international standard second. The International Standard Second was launched at 0:00 UTC on January 1, 1972, ending the situation in which previous time bases were obtained through complex measurements and calculations of the movements of celestial bodies.
The definition of “second” has nothing to do with the movement of celestial bodies. Since then, time measurement work in various countries has been transferred from astronomical departments to metrology laboratories.
2. Globally unified timekeeping method – zone time system
(1) Time zone
Before the establishment of the zone time system, there were no certain guidelines for clocks around the world. It is said that in 1880, there were three clocks at the Buffalo train station in New York State: one showed the local time in Buffalo, one showed the time in New York City, and the other showed the time in Columbus, Ohio. The confusion can be seen Just imagine.
In 1879, Canadian railway engineer Volemin first proposed the concept of “time zones” in the world. In 1883, the American Railway Bureau held a meeting and decided to divide the country into 4 time zones, with each time zone differing by 1 hour. This is The earliest time zone system.
In 1884, at the International Meridian Conference in Washington, it was decided to extend the zone time system worldwide. watches home watch custom
(2) Zone time system
1.Zero time zone
Starting from the zero longitude passing through the Greenwich Observatory in London, England, it stretches 7°30′ to the east and west for a total of 15°. The zero longitude is the central meridian of the area. In the East time zone, it is from 7°30′ East longitude to 22°30′ East longitude, and 15° East longitude is the central meridian of the time zone; in the West time zone, it is from 7°30′ West longitude to 22°30′ West longitude, and 15° West longitude is the central meridian of the time zone. central meridian; and so on. Obviously East 12th District and West 12th District overlap
2.Zone time system
Every 15 longitude ranges on the earth are regarded as a time zone (that is, the longitude traveled by the sun in 1 hour), so that the entire earth’s surface is divided into 24 time zones. The “zone time system” solves the confusion of time in various places to a great extent, so that there are only 24 different times in the world, and because the time difference between adjacent time zones is exactly 1 hour, so the time difference between different time zones Time conversion becomes extremely simple.
This time zone system has been used around the world for over 100 years.
3. Commonly used timing nouns
Universal time
Universal time is also called Greenwich time. The International Meridian Conference held in Washington in 1884 decided to locate the meridian passing through the Greenwich Observatory in England as the zero degree meridian (also known as the prime meridian). The zero time zone uses the local time passing through this meridian as the standard time.
Note: Greenwich Mean Time represents 12:00 noon; the dateline represents 24:00 midnight.
International Date Line
Referred to as “Dateline”
After universal time and universal time zones are determined, where to start calculating a new day on earth has become a new question.
Before the “date line” is determined, we often encounter such a problem: According to the zone time system, when Beijing is 20:00 on Monday, extrapolating eastward, the time in the East 12 time zone should be 0:00 on Tuesday; Extrapolating westward, the time in the 12 West time zone should be 24:00 on Monday. So at the same moment, in the same time zone, is it 0:00 on Tuesday or 24:00 on Monday?
In order to solve this problem, international organizations held another meeting and finally decided to use a line near the 180° longitude as the “date line”. In order to avoid some islands, the date line is no longer a straight line and does not pass through any land except Antarctica.
Each day on Earth begins at the dateline, which is the earliest point of each day on Earth.
The date change rules were also set at the 1884 International Conference: when moving from the west of the date line to the east of the date line, the date will be counted as less than one day (for example, if June 8 passes the date line, the date should be turned back to June 8). On the 7th of the month, the next day is still counted as June 8): and when moving from the east of the date line to the west of the date line, the date is counted as one extra day (for example: if August 9 crosses the date line, then the date should be turned over. By August 10th, the next day should be counted as August 11th).
With the date line, the problems raised above are easily solved. If everyone abides by this rule, there will be no confusion about dates and days around the world.
Leap second
The “leap second” was born after the implementation of the “International Standard Second” reference for atomic time in 1972. The purpose is to compensate for the difference between the scientific time reference and the speed of the earth. That is, every few years, 1 second is added or subtracted from the standard time to make the scientific standard time consistent with the movement of the earth.
The leap second is generally scheduled to occur within the last minute of December 31st of the current year or the last minute of June 30th of the current year. At what time of year the leap second will take place, the information will be released uniformly by international organizations.
The leap second adjustment is due to the small difference between atomic time and universal time. When the difference between the two time systems exceeds 0.5 seconds, one second needs to be added on June 30 or December 31 of each year. The leap second adjustment will not have any impact on the daily lives of ordinary people.
World clock
The world clock is designed based on the principle of the zone time system. In modern times, many clocks have a world time function, that is, the 24-hour hour circle moves clockwise, and its transmission ratio to the hour wheel is 1:2; the hour hand rotates 2 times, and the 24-hour hour circle only rotates once. , is a world clock with a relatively simple structure.
The outermost circle of the world clock is the geographical circle, which is divided into 24 equal parts in the order of time zones. In each equal part, 1~2 important cities in each time zone are marked. Generally, the city name on the place name circle does not change, but the time can be adjusted. https://watcheshome.com/
