Encyclopedia of popular science knowledge: "Time Knowledge"

Chapter 10 Time's Fun Story (3)
To the west of the date line is "today" and to the east of the line is "yesterday".When ships and planes sail in the Pacific Ocean, when they cross the date line from west to east, one day will be subtracted from the date, and the calendar with the previous day will seem to "return" the lost time; if passing the date line from east to west The boundary line is about to tear off a page from the calendar immediately. Before that day is over, it is time to say goodbye. Time seems to be "missing" all of a sudden.

If people like to have two festivals or birthdays a year, they only need to go to Fiji or Tonga on the festival or birthday, and go to Western Samoa the next day.Therefore, it is completely possible to go back in time and travel to "yesterday".

cutting the time that can't be clear

In the 4th century AD, the ancient Roman philosopher and theologian St. Augustine once said a famous saying meaningfully: "What is time, if no one asks, I know; but if I need to explain, I don't know." .”

For the invisible, intangible, but always aware of time, it is indeed an eternal mystery. All walks of life have their own mottos:

Workers say: time is wealth.

Farmers say: time is food.

People's Liberation Army soldiers tell people: Time is victory.

Many students think: time is knowledge.

Entrepreneurs often emphasize: time is money.

And doctors know that time is life.

In fact, time is both a scientific question and a very deep philosophical question.

It is said that when the Russian poet Marsak first visited England in 1914, he did not have a good grasp of English. Once he forgot to bring a watch when he went out on the street, so he had to ask passers-by.He politely asked an elder: "Please tell me, what is time?" The man was stunned, and after a while he said: "This is a philosophical question, why are you asking me?"

Some people regard clocks as time, which is a great misunderstanding.A clock is just a tool for keeping time.Before the advent of clocks, time also kept passing.

In ancient times, people "worked at sunrise and rested at sunset".This is the hazy concept of time, but intuitively so.The Roman poet Platus wrote: "My belly is my chiming clock.

It is the best and most accurate of all timepieces. "

Even with a clock, there are at least two problems.The first is how to count from the moment when an event occurs.For example, if my country's first man-made satellite "Dongfanghong 1" was launched into the sky, it would be April 1970, 4 if the AD was used as the starting point, but it would be the 24th day since the founding of the People's Republic of China.Just like Wuxi is 7510 kilometers west of Suzhou, but if the starting point is changed to Shanghai, it is 42 kilometers.

Second, is how to determine how much time has elapsed between two events.The same rope is measured with different "rulers", and the value must be different.

If the meter ruler is 1.5 meters, then the market ruler is 4.5 feet, and the foot meter is 4 feet 11 inches.

Time also has a "unit problem", how many times have you been hungry?How many pages did you read?Or use the sun rises a few times?How many times does the earth revolve around? ....

Time, length, and quality are the three basic elements of all physical units, which are closely connected with space and motion and cannot be separated.The issue of time is still an important part of astronomy. Even today, time measurement and time service are still one of the important tasks of some observatories.

my country's Shaanxi Astronomical Observatory is responsible for the important task of releasing time signals on time.

In order to accurately measure the time, people have spent a lot of energy, and this kind of exploration and practice has greatly promoted the development of astronomy and even the entire science.

Poker and the Calendar

Playing poker is a recreational activity that can eliminate fatigue.The French said that in the 14th century, after the French Emperor Charles VI fell ill, he was depressed all day long. In order to cheer up Charles VI, a French scholar invented this kind of card.According to the Belgians, Belgian poker predates France by 13 years - the pastime dates back to 1379.But recently, Carter, an authority in the history of printing in the United States, believes that the earliest ancestor of playing cards is the "Leaf Play" in the Song Dynasty of China, which was later brought to Europe by Marco Polo...Of course, playing cards are also used as gambling tools. There are many people who are fascinated by these 54 cards, and even go bankrupt.

But in any case, the merits of poker outweigh the demerits.In the age of cultural backwardness, it once played the role of a textbook.French Cardinal Machaelin was worried that the young King Louis XIV would not study hard because he was too playful, so he compiled a set of "educational poker".There is also a poker "K" with a map of Europe, "Q" with a map of France, and "J" with a map of Spain.In addition, Greece, the United Kingdom... etc. have all played poker, which has achieved very good results.Poker was once very popular in Europe.

The connection between playing cards and the calendar However, the best combination with playing cards is undoubtedly the calendar in astronomy.In fact, its evolution and development are influenced by the calendar.You see, there are 54 playing cards in a set, and the 52 cards are exactly the number of weeks included in a year; the big king and the little king represent the two most important celestial bodies in the sky: the sun and the moon.Looking at its color, spades, hearts, grass flowers, and diamonds just represent the four different seasons of spring, summer, autumn and winter: spades represent the green leaves that germinate in spring, hearts symbolize the sweet peaches in summer, grass flowers and withered yellow leaves. The fallen leaves are similar, and the squares are the glittering icicles of severe winter. The only two colors in the card are red and black, which symbolize the alternation of day and night: red represents day and black represents night.

Each season is on average 13 weeks long, so each suit has 13 cards.Calculated by points again, if J is regarded as 11 points, Q is regarded as 12 points, K is regarded as 13 points, and A is regarded as 1 point, then the total points of each suit are 1+2+3+...+12+13=91, which means Exactly the number of days contained in a quarter (there may be a difference of one day in the calendar).The total number of points of the whole playing card is 91*4=364, plus Xiao Wang's point is 365, which is equivalent to the number of days in an ordinary year, if run into a leap year, then can add that point of King's.

The common Gregorian calendar (Gregorian calendar) is based on the apparent movement of the sun, which passes through the signs of the zodiac in sequence throughout the year.And there are exactly 12 big cards with heads in the playing cards - J, Q, K of four suits, which just represent the 12 constellations on the zodiac:
Pisces, Aries, Taurus (spring sun sign), Gemini, Cancer, Leo (summer sun sign), Virgo, Libra, Scorpio (autumn sun sign) and Sagittarius, Capricorn, Aquarius (winter sun sign) .

Of course, the calendar and playing cards cannot be equated after all, for example, the "month" in the Gregorian calendar

There is no trace of it in the playing cards.In fact, the "month" in the modern Gregorian calendar itself is somewhat "nondescript". It has nothing to do with the sun's east rising and west setting, and it has nothing to do with the moon's profit and loss. It is just a medium-length time unit artificially. No wonder It's about to be ignored in poker.

From what year should the 21st century be counted?

Does the 21st century start from 2000 or 2001?This is a long-disputed issue.

There has been an international debate on how to divide the century, and the focus of the debate is the relationship between "century" and "year".In our country's newspapers and periodicals, "age"

一词的应用十分广泛，无一例外都从“0”年起始。我国天文学界专家学者认为，如果主张2000年为21世纪的第一年，那么2000—2009年则可称为21世纪的初十年代；如果主张2001年为21世纪的第一年，那么2000年则无法纳入任何年代的一年。因此我国天文学者认为世纪应从“0”开始，2000年应是21世纪的第一年。

How long is a day on the moon
While the moon is revolving around the earth, it is also constantly rotating from west to east.Therefore, the sun also rises in the east and sets in the west on the moon.However, this is completely different from the "sunrise" and "sunset" scenes seen on the earth.

On the moon, after the sun rises from the east, it takes more than 180 hours to rise to the mid-heaven; it takes another 180 hours to move from the mid-heaven to the west "horizon" and set; Count as a "day and night".To be precise, a day and night on the earth is 360 hours, 23 minutes and 56 seconds; a "day and night" on the moon is as long as 04 days!
When the sun comes out, because there is no atmospheric barrier around the moon, the sun seen in "daytime" is thousands of times brighter than the sun seen on the earth.The temperature of the lunar surface can reach 127°C. Even in "daytime", on the lunar surface, you can still clearly see the dots of stars in the dark sky and the incomplete earth due to the change of "terrestrial phase"!

No sooner had the sun set than night fell over the moon—the long night had begun! The "dark night" lasts for about two weeks, and the temperature drops to -183°C.In the dark night sky, you can see a huge "bright moon" - the earth reflecting the sunlight hangs high in the sky, "shine brightly", the brightness is 80 times brighter than the moon we see on the earth!
It is ideal to set up an observatory on the moon, because there is no interference from the atmosphere and dust, and the stars can be observed clearly no matter day or night, which is much more advantageous than on the earth and far superior to that on artificial satellites.

有趣的10点10分35秒有趣的10点10分35秒不知你注意过没有，当你在钟表店选购钟表的时候，或是观赏橱窗里摆着的钟表样品的时候，你会发现所有停着的钟表都是在10点10分35秒上，你知道这是为什么吗？

It turns out that the positions of the hour hand, minute hand, and second hand at this time give people a very coordinated feeling, basically dividing the surface into three equal parts, so that customers can clearly see the structure of the watch.In addition, the hour hand, minute hand, and second hand of this time are like a person cheering and triumphant, jumping towards you. The first letter of the word "victory" in English is "V", and these three needles are placed in the shape of "V".Since clocks and watches were produced in Europe, designers and manufacturers took 10:10:35 as the best time to display time.

How is one second determined?
The second is the smallest unit of time measurement in people's daily life. We are familiar with it just like we are familiar with kilograms and meters. No one does not use it.But how long is 1 second?How is the fleeting 1 second determined?This is an interesting question.

Some people may say, isn't 1 second the time when the clock "ticks"?Yes, generally speaking, the tick time is 1 second.But is it the same for several clock ticks?Just the same good clock, does it tick the same time in winter, summer, morning, and evening?Know through precise measurements that they are not all the same.

Practice has proved that the length of a few seconds is not the same.The second length of the same clock also changes with time, so, which second length is the standard?There is no common second in the world, and it is impossible to have a common language in time.

Seconds, can we uniformly manufacture a "prototype" in the world like meters and kilograms, and everyone uses it for calibration.

We know that the meters and kilograms used by people were originally passed down from the "international prototypes" made of platinum-iridium alloys. These prototypes are stored in special places: the temperature remains the same in all seasons, and the vibration and impact are minimized... Time Woolen cloth?It can't be seen, touched, or locked, so where is the original time device?

Nature provides human beings with a resting place and a primitive time reference.People still focus on the macroscopic world first, and study the rotation and revolution of the earth to determine the length of a second.With the deepening of human understanding to the microscopic world, after the invention of the atomic clock, it is indeed possible to preserve the standard second length in the laboratory just like the international prototypes of meters and kilograms.

Use the rotation of the earth to determine the length of a second—the sun shines on the earth during universal time, and the earth is constantly rotating from west to east. This is the "huge clock" provided by nature for people.Unlike our ordinary clocks and watches, when this huge clock is moving, the "hands" do not move, and the "dial" rotates.The pointer is a plane determined by the two poles of the earth and the sun, the dial is the earth itself, and the longitude on the earth is the scale of the dial.When the earth rotates, each point on the earth passes through the "pointer" one by one. Isn't this just a big clock?

This big clock turns once every 24 hours, which is the most familiar time unit "day".

With a clear day length, the month length and year length can be calculated by accumulating, and the hours, minutes, and seconds can be obtained after equalization.

Thus, the length of a second can be determined with this big clock, which is 1/86400 of the length of a day.The "universal time" commonly used in the world is defined according to this earth rotation period.

The earth rotates and the sun does not move. According to the principle of relative motion, looking at the sun from the earth is like the sun moving around the earth.Astronomers define the time required for the sun to pass through the longitude (meridian) of a fixed point on the surface of the earth twice as one day, which is the "true solar day", and 1/86400 of the true solar day is the second length of the true solar day.

However, the revolution speed of the earth is not uniform.Because the orbit of the earth moving around the sun is not a circle, but an ellipse, and the sun is located at a focus of the ellipse.In addition, the rotation axis of the earth is not perpendicular to the plane of the earth's revolution orbit; this makes the speed of the sun's position change reflected by the earth at different places in the revolution orbit.In this way; the true solar day has a long and short, the longest is December 12, and the shortest is September 23.The length of a true solar day differs by as much as 9 seconds.In view of this situation, the use of true solar days to determine the length of the second appears to be inaccurate.Therefore, people use the average length of the real solar day - "average solar day" to determine the second.The time reference determined by such a mean solar day is called the zero-type universal time, and it is recorded as UT16.

Similarly, 1/86400th of the mean solar day is the second of the mean solar day, that is, the second length of universal time zero, and the second length of UT0.

For this reason, an international academic conference was held in Paris, France in 1886, which accepted the research results of the American astronomer Newcomb and came up with a strict definition of "average solar day", which led to the concept of universal time.

With the development of science and technology, people realized that not only the earth's revolution speed is not uniform, but also the earth's "rotation axis"

position is also changing.The position of the two poles (the South Pole and the North Pole) on the surface of the earth is also changing, and we usually call this phenomenon "polar change" or "pole shift".

We can measure the extreme position change more accurately.A better method is to set up many observation stations at points with the same latitude and different longitude, and analyze the measurement data provided by these observation points to obtain the change of the pole position. The range of the change of the pole position is about 20 square meters. .

Will such a small change affect the timing accuracy?

Yes, because the latitude and longitude of all parts of the world are determined based on the pole as the origin. Due to the movement of the pole, the latitude and longitude of all parts of the earth will inevitably change, and the corresponding time will also change.Since this effect is not the same in different parts of the world, the second length of the time base reflected in UT0 is also not the same in all parts of the world.

Another reason why the second length of UT0 varies around the world is that the North Pole does not always point north.The earth "precesses" due to the attraction of the moon (the earth also precesses due to the attraction of the sun, because the sun is too far away from us, so the precession is very small), the result of the earth's precession makes the earth's axis point to the direction of the sky It is no longer a point, but a circle.It takes 25800 years for this circle to complete one revolution!Now the north pole of the earth's axis points to the vicinity of Polaris, and after 12000 years it will point to the brightest star in the sky in the northern hemisphere—Vega, and Vega will become Polaris at that time.

To remove the effect of pole shifts, we take an average value called "flat north pole".The world time determined with the flat North Pole as the origin is called the first world time and is denoted as UT1.

UT1=UT0+△λ这里的△允是对UT0的修正量。对UT0修正以后得到的UT1在世界各地则是相同的。这样，UT1的秒定义有了更为普遍的意义，便于应用了。

After the above-mentioned correction of extreme position changes, the second length of UT1 is still not uniform enough.It turns out that various seasonal changes still play a role in it.Various factors that change with the seasons, such as the influence of monsoons, the growth of plants, and the distribution of lightning, will cause seasonal changes in the earth's rotation.

Some people have calculated the monsoons; every summer they blow from the ocean to the land, and in winter they move back to the ocean from the continent. The weight of these winds is unbelievably large, as many as trillions of tons!Such a large weight is moved from one place to another, and then moved back from another place after a while, the earth's center of gravity changes, and as a result, the earth's rotation speed also changes accordingly.This variation is produced by the effects of seasonal changes.

The UT1 that corrects the seasonal changes is called the second world time and is recorded as UT2.It can also be said that adding the correction amount to the first world time UT1 is the second world time, that is:
UT2=UT1+△Ts=UT0+△λ+△Ts第二世界时UT2部分改善了自转速度的不均匀，使秒长的均匀性有了改善。但由于地球的自转还有不规则变化和长期变化，所以UT2这个时间基准还是不够理想的。

The irregular change of the earth's rotation is manifested in the fact that the earth's rotation speed will "jump" every few decades. In some years, it rotates faster, and in some years, it rotates slower.

The long-term change of the earth's rotation is manifested in the last 2000 years. Every 100 years, the length of the day increases by 1.6 milliseconds, that is, the earth's rotation tends to slow down.

(End of this chapter)