Solar Eclipse and Political and Cultural Life

How is a solar eclipse formed?

The so-called "eclipse" refers to an astronomical scene in which one celestial body is completely or partially obscured by another celestial body or its shadow. There are three main types of solar eclipses: total solar eclipse, partial solar eclipse and annular solar eclipse. The principle of solar eclipse is that some areas on the earth are covered by the shadow of the moon. The solar eclipse must occur on the first day of the new lunar month (Shuo). This is because only on that day will the moon appear on the line between the sun and the earth, making it possible for the moon to block the sun and form a solar eclipse. Similarly, the lunar eclipse must occur on Wangri, which is the fifteenth day of the lunar calendar.

You may ask, why is there not a solar eclipse on the first day of every month, and why is there not a lunar eclipse on the fifteenth day of every month? This is because in addition to the above conditions, there are other factors that affect the occurrence of solar and lunar eclipses. We call the Earth's orbit around the Sun the ecliptic, and the Moon's orbit around the Earth the ecliptic. The ecliptic plane and the ecliptic plane are not the same. There is an average angle of 5°09′ between them, and it changes at any time. A solar eclipse only occurs when the moon moves near the ascending and descending nodes of the ecliptic and ecliptic.

Types of solar eclipses

There are three types of solar eclipses: partial solar eclipse, annular solar eclipse and total solar eclipse. When the moon covers part of the sun, it's called a partial solar eclipse. The moon only covers the central part of the sun, and a ring of solar surface is exposed around the sun, which is like a halo, which is called an annular solar eclipse. When the sun is completely covered, it is called a total solar eclipse. The occurrence of these three different solar eclipses is related to the changing positions of the sun, moon and earth, and is also determined by the changing distance between the moon and the earth.

The moon is much smaller than the sun, its diameter is about one-fourth of the diameter of the sun, and the distance between the moon and the earth is almost one-fourth of the distance between the sun and the earth, so Seen from the Earth, the moon is almost the same size as the sun, so it can cover it up and cause a solar eclipse.

The orbits of the earth and the moon are ellipses. The distance between the sun and the earth, or the distance between the moon and the earth, is not fixed. Sometimes it is farther away, sometimes it is closer, so The length of the moon's umbra is also different. The longest umbra of the moon is 379,660 kilometers and the shortest is 367,000 kilometers. The distance between the earth and the moon is 356,700 kilometers at the shortest and 406,700 kilometers at the farthest. If the moon's umbra is larger than the distance between the earth and the moon at a certain moment, a total solar eclipse can be seen on the earth swept by the moon's umbra. If the Moon's umbra is smaller than the distance between the Earth and the Moon, and the tip of the Moon's umbra cannot reach the Earth's surface, then an annular solar eclipse can be seen in the area swept by the small shadow cone (called the pseudo-umbral) extended from the shadow tip. . A partial solar eclipse can be seen in the area swept by the lunar penumbra. The closer to the total eclipse area in the partial eclipse area, the greater the degree of partial eclipse. Where the moon's umbra and penumbra are not swept, the solar eclipse is not visible at all.

The following is the number of solar eclipses that have occurred worldwide in this century (1901-1999):

Number of types

Partial eclipses 78

Total solar eclipse 71

Mixed eclipse 6

Total 228

The process of solar eclipse

The process of a solar eclipse can be divided into five stages, and only a total solar eclipse has the entire process. Partial solar eclipses and annular solar eclipses do not have both eclipse and light generation. First waning: the moment when the sun and the moon first cut outward, and the west side of the sun's photosphere just cuts into the east side of the moon. Eclipse: The moment when the sun and the moon come in contact for the first time and the sun's photosphere is completely obscured by the moon. Eclipse: The moment when the distance between the center of the moon and the center of the sun is smallest. Photogenesis: The second involution between the sun and the moon, the moment when the sun's photosphere just emerges from the west side of the moon. Compound circle: the second circumcision between the sun and the moon, the moment when the sun's photosphere has just completely left behind the moon. The initial loss, eclipse, birth of light, and re-circulation are also called the first, second, third, and fourth contacts respectively.

The rules and cycles of solar eclipses

Since the revolutions of the earth around the sun and the moon around the earth and the movements of the yellow and white nodes are regular, they will occur at certain intervals. A roughly similar solar and lunar eclipse. As early as ancient times, based on long-term statistics of solar and lunar eclipses, the Babylonians discovered that the cycle of solar and lunar eclipses is 233 synodic months, which is 11 and 1/3 days in 18 years, which is the Saros cycle.

How to observe a solar eclipse?

When observing a solar eclipse, do not look directly at the sun with your eyes. Decades ago, dozens of people in Germany went blind just because they looked at the solar eclipse with their eyes! Why can watching a solar eclipse directly with your eyes hurt your eyes or even cause you to go blind? It turns out that sunlight and its invisible infrared rays contain a large amount of thermal energy, which will generate a large amount of heat when absorbed by objects. Everyone has this experience. If you look directly at the sun with your eyes, even if you only look at it for a short moment, your eyes will be greatly stimulated. Your eyes will be dim for a long time, and it will be difficult to recover. This is because there is a crystal in the eye. It can act as a condenser. If you look at the sun, the sun's heat energy will be concentrated on the retina at the bottom of your eyes, which will make your eyes dazzling; if some time passes, the retina will be burned and you will lose your vision.

When a solar eclipse occurs, it is a partial eclipse most of the time. The moon only blocks part of the sun, and the remaining part remains the same as usual. Therefore, if you look directly with your eyes for a long time, it will also burn your eyes. Usually a piece of blackened glass can be placed in front of the eyes (or the glass can be placed on fireworks to blacken it). The thickness of the ink layer should be uniform so that the eyes can see the sun through it and turn it into a bronze color. It does not look dazzling but can be seen clearly. Sometimes they also pour water with ink into a basin and watch the sun reflected in the water. Some also took fully exposed photo negatives and stacked them together to look at them. People who use telescopes to watch must add a filter in front of the lens. The principle is also to weaken the sun's rays so that it does not burn the eyes. But in any case, you must not put your eyes close to the telescope to look directly at the sun, otherwise your eyes will be burned. When not observing, do not point the telescope or camera at the sun, and cover the lens with a cap to prevent the lens from absorbing excessive heat and causing it to burst.

Most of the total solar eclipse zone that will occur on July 22, 2009 is in the Pacific Ocean, and almost all of it is located on land in China, passing through Sichuan, Chongqing, Hubei, Anhui, Jiangsu, Zhejiang, Densely populated provinces and cities such as Shanghai, while some other provinces in China can only see partial solar eclipses under different conditions. The total solar eclipse can be seen in Hangzhou, Huzhou, Jiaxing, Ningbo, Zhoushan, and Shaoxing in the solar eclipse belt of Zhejiang, China. Other cities can also see partial solar eclipses of varying degrees. Even in the southernmost part of Zhejiang, you can see a partial solar eclipse with an eclipse of about 91.4%. Among them, Zhoushan is the easternmost city in the total solar eclipse zone. The city can be observed for up to 2 hours and 40 minutes; secondly, there is no obstruction on the sea surface, while other cities are mostly located in basins with many mountains blocking the observation; thirdly, when a total solar eclipse occurs, Zhoushan has the largest solar altitude angle. The best observation effect. According to research by the International Astronomical Organization, Daishan and Shengsi counties in Zhoushan City are very close to the center line of the total solar eclipse belt, which can be said to have unique geographical advantages. The next visible total solar eclipse in my country will occur in 2015 and will be limited to the northern region. For people in Zhejiang Province, the next total solar eclipse at home will be on June 9, 2309, and they will never be able to see it again in this lifetime. Therefore, this total solar eclipse is an excellent opportunity for people in Zhejiang Province. Don't miss it.

Among the major observation sites in Zhoushan City, "Shengsiji Lake" has the highest latitude and is closest to the center line of the total solar eclipse zone. The total solar eclipse also lasts the longest, making it the best observation site.

Do not observe directly

Medical experts point out that "solar retinitis", which causes burns to the retinal macula due to its ultraviolet and infrared rays caused by looking directly at the sun for a long time, is almost impossible to treat. . The macula is the most sensitive part of the retina, where it focuses light and makes images clear. Once burned, the retinal macula will never recover. You may not feel anything when you are burned, but reactions will occur a few hours later, and in severe cases, you may become blind. When viewing a total solar eclipse, the first thing to note is: Never look directly at the sun with the naked eye or any optical equipment (such as a telescope, etc.)! This is not just a suggestion, but a very serious warning. How to avoid some accidents? The following methods will be introduced to you.

(1) Quick and easy observation method

In fact, the recommended method is just to use two pieces of white paper. Use a piece of white cardboard as a screen, poke a pinhole in the other piece of cardboard, and lift the pinhole cardboard as far away from the screen cardboard as possible. The further apart the two cardboard sheets are, the larger the image formed.

Of course, there is a simpler way, which only requires the help of your own hands. Raise your hands with your fingers perpendicular to each other and overlapping each other, so that your hands form a network with many small holes. The small hole can be used as a simple imaging hole.

(2) Homemade observation glasses

Protective glasses require a special pair of glasses. There are such special sun protection glasses on the market, and the price is about 5 yuan. You can also make your own observation glasses:

1. Use smoke to apply a thick layer of carbon on ordinary sunglasses, the darker the better;

2. Apply a thick layer of black on the glass Ink, which dries to act as a lens.

Observing a partial eclipse: When observing or taking photos, be sure to wear sunglasses and add appropriate filters.

Observing Bailey's beads and solar prominences: The key to taking good photos of Bailey's beads and solar prominences is to grasp the timing, because they are fleeting and can last only a few seconds at most, so we must be in the moment of the eclipse. Begin to closely monitor the frosted glass on the viewfinder one or two minutes before the light is generated. As soon as you see Bailey's beads and solar prominences, expose decisively without hesitation for a moment. Be careful not to forget to remove the filter.

[Edit this paragraph] Introduction to solar eclipse

A solar eclipse is when the moon moves between the sun and the earth. If the three are exactly in a straight line, the moon will block the sun's direction. The light of the earth and the dark shadow behind the moon just fall on the earth, and a solar eclipse occurs at this time. People in the moon shadow on the earth began to see the sunlight gradually weakening, and the sun's surface was covered by a round black shadow. When the sky turned dark, the brightest stars and planets could be seen in the sky. After a few minutes, from Sunlight gradually emerged from the edge of the moon's dark shadow, and began to glow and become round again. Because the moon is smaller than the Earth, only people in the moon's shadow can see the eclipse. A total solar eclipse occurs when the moon completely blocks the sun, a partial solar eclipse occurs when it partially blocks the sun, and an annular solar eclipse occurs when it blocks the central part of the sun.

The duration of a total solar eclipse will not exceed 7 minutes and 31 seconds. The longest annular solar eclipse lasts is 12 minutes and 24 seconds. In order to delay the observation of a total solar eclipse, a French astronomer flew a supersonic aircraft to chase the moon's shadow, extending the observation time to 74 minutes. Our country has the oldest records of solar eclipses in the world, with exact records of solar eclipses dating back more than 1,000 BC.

Scientific explanation

Solar and lunar eclipses are typical examples of light propagating in straight lines in celestial bodies. A solar eclipse does not occur every time the moon moves between the sun and the earth. Two conditions need to be met for a solar eclipse to occur. First, solar eclipses always occur on the first day of the new moon (the first day of the lunar calendar). Not all solar eclipses are bound to occur on new moons, because the moon's orbit (the ecliptic) and the sun's orbit (the ecliptic) are not on the same plane. The angle between the ecliptic plane and the ecliptic plane is 5°9′. If on the new moon, both the sun and the moon move near the intersection of the ecliptic and the ecliptic, and the sun is at a certain angle from the intersection (solar eclipse limit), a solar eclipse will occur. This is the second condition that must be met.

Since the orbits of the moon and the earth are not perfect circles, the distance between the sun and the moon and the earth is sometimes closer and sometimes farther away, so the shadow formed by the sunlight being blocked by the moon can be divided into the main shadow on the earth. , pseudo-umbra (formed when the moon is farther from the earth) and penumbra. Observers can see a total solar eclipse within the umbral range; an annular solar eclipse can be seen within the pseudo-umbral range; and only a partial solar eclipse can be seen within the penumbral range.

There are many mountains on the surface of the moon, and the edges of the moon are uneven. When the valley on the edge of the moon fails to completely block the sun at the moment of eclipse or solar radiation, the unblocked part forms a luminous area, like a crystal "diamond"; the surrounding light red aperture forms the "ring" of a diamond ring. , overall, it looks like a diamond ring inlaid with bright gems. Sometimes many particularly bright rays or light spots are formed, as if a string of pearls are inlaid around the sun, called Belly beads (Belly is a French astronomer).

Whether it is a partial solar eclipse, a total solar eclipse or an annular solar eclipse, the time is very short. The area where you can see a solar eclipse on the earth is also very limited. This is because the moon is relatively small, and its umbra is also relatively small and short. Therefore, the umbra does not sweep over a wide area on the earth and does not last long. Because the moon The average length of the umbra (373,293 kilometers) is smaller than the average distance between the Moon and the Earth (384,400 kilometers). For the entire Earth, annular solar eclipses occur more often than total solar eclipses.

The main reason why a total solar eclipse is valued is that it has great astronomical observation value. Many major astronomical and physical discoveries in the history of science have been made using the opportunity of a total solar eclipse, and only through this opportunity. The most famous example is a total solar eclipse in 1919, which confirmed the correctness of Einstein's general theory of relativity. In 1915, Einstein published the general theory of relativity, which was considered extremely difficult to understand and extremely incredible at the time. This theory predicted that light would bend in a huge gravitational field. The strongest gravitational field that humans can come into contact with is the sun, but the sun itself emits very strong light. It is impossible to tell whether the faint starlight in the distance has turned when it passes near the sun. But if a total solar eclipse occurs and the sun's rays are blocked, you can measure whether the light has turned and how far it has turned. The opportunity appeared in 1919, but the total eclipse was in the South Atlantic, which was very remote and difficult. British astronomer Eddington set out with an enthusiastic and curious observation team. The observation results were very consistent with Einstein's pre-calculated results, and the theory of relativity has since been recognized by the world.

In China, the first two total solar eclipses could only be seen in remote areas. The first time was in 1980, which was only visible in the Ruili area of ??Yunnan on the China-Myanmar border. At that time, the author had just entered junior high school and was an avid young astronomy enthusiast. Unfortunately, he had no financial means and could only feed his addiction through the magazine "Astronomy Enthusiasts". The other time was after the Spring Festival in 1997, which was visible on the Sino-Russian border and the northernmost point of China, Mohe. That time, the author went to interview on the order of the newspaper, and at the same time, he also fulfilled his childhood dream. The scale of that observation was beyond imagination. Astronomers and astronomy enthusiasts from all over the world crowded a small town in northern Xinjiang, which is usually inaccessible, even more lively than the New Year. Because the number of people greatly exceeded the reception capacity of the town, people only Can camp on trains and buses. It was still winter there at that time, and the temperature during the day was about minus 25 degrees Celsius, and at night it could reach minus 40 degrees Celsius. The dripping water turned into ice, and people couldn't even find water to wash their faces and gargle. Despite this, none of the observers regretted it, and none of them was not excited. They all regarded seeing the total solar eclipse with their own eyes as a rare and precious memory in their lives. Astronomical phenomena such as total solar eclipse do not have any direct relationship with people's daily life, eating, drinking and diarrhea. However, it represents an ultimate humanistic concern, an extreme love for nature, and an eternal curiosity and awe for the iron laws of nature that govern all things. It is indispensable for a country and a nation. These cares, these loves, these wonders, these awes.

[Edit this paragraph] History of solar eclipses

1: China has a long history of observing solar eclipses. Someone observed a solar eclipse as early as 1948 BC. China had the most advanced astronomical observatory at that time more than 2300 BC. China has always attached great importance to the prediction of solar eclipses. It is said that an astronomical official in the Xia Dynasty was beheaded as a warning to those who neglected their duties because he was indulged in wine and debauchery and failed to report a solar eclipse.

China has the earliest, most complete and richest solar eclipse records in the world. There are more than 1,000 records of solar eclipses in historical materials (excluding oracle bone inscriptions) from ancient books (up to the Qing Dynasty) alone. The earliest record was a solar eclipse that occurred in 1948 BC. The "Book of Songs" records in detail the solar eclipse that occurred on September 6, 776 BC: "At the turn of October, the first day of the lunar month was Xin Mao, and the sun had an eclipse." The world's astronomers generally recognize that ancient Chinese solar eclipse records It has the highest degree of credibility and has left precious scientific and cultural heritage to the world. The Xia, Shang and Zhou dynasties in ancient China have a long history and lack precise written records, so it is difficult to accurately date them. Solar eclipses are like a very accurate historical clock, which can help determine the time of some historical events.

2: A solar eclipse stopped a war in the ancient West. The most famous story in the West was recorded in 585 BC. The Mitis and Libyan tribes were fighting. In the middle of the battle, the sun suddenly disappeared. The people of the two tribes were afraid of the coming disaster, and finally reached a beautiful result - the two tribes made peace and intermarryed. Regarding the view of the solar eclipse phenomenon, except for the Tahitians who regard the solar eclipse as a positive meaning, other countries interpret it negatively. For example, in more than 600 BC, when Athens was attacking a certain tribe, it was too afraid to move forward because of an eclipse. Because it delayed the attack, it allowed the enemy to take advantage of this period to prepare. As a result, when the Athenian army attacked the enemy time, but was defeated.

3: According to Shen Baofeng, an outstanding historical and cultural scholar and young songwriter in Handan City, Hebei Province, who has long studied the solar eclipses in ancient tombs of the Han Dynasty, he found that various ethnic groups have different views on total solar eclipses, such as ten dogs eating the sun, wolves chasing the sun, etc. Different explanations and their own solutions. In ancient China, people used to beat gongs and drums to deal with it; since the duration of a total solar eclipse is usually very short (at most seven and a half minutes), the sun may reappear immediately after people beat it, thus eliminating the need for People panic. China has recorded solar eclipses very early. Many stones were excavated from tombs in the Han Dynasty. Many figures of the sun, moon and stars were carved on these stones. One of the paintings had "the sun and the moon combined", which means that the sun and the moon are superimposed on each other. Together, this is the record of the solar eclipse at that time. The Chinese scientific explanation for a solar eclipse is that yin invades yang. China has known for a long time that the moon, which is regarded as "yin", blocks the sun, which is regarded as "yang", causing a solar eclipse. In ancient times, there was a saying that "when the moon is waxing, there will be an eclipse." This means that lunar eclipses always occur when the moon is full. When a solar eclipse occurs, the ancient Chinese court will also take action; the Chinese believe that the sky represents nature, and the sun has the highest status in nature. The emperor is called the Son of Heaven, which means that he is sent by God to manage the people. Since the sky represents the emperor's father, it will warn its earthly agent, the emperor, through phenomena on the surface of the sun, telling him clearly what he has done wrong, what things he should be careful about, etc.; thus, through various signs, Come out, the solar eclipse is a situation that is often exploited. According to the records of Bi Zhen Hall in the ancient book, whenever a solar eclipse occurred in the Han Dynasty, the emperor would not go to the main hall for morning court, but to the small hall next to the side hall for morning court, and everything was kept simple. According to legend, a solar eclipse is called "Tengu swallows the sun." The scientific explanation for "Tengu swallows the sun" is a solar eclipse. A solar eclipse is a classic example of light traveling in a straight line through a celestial body. Since the orbits of the moon and the earth are not perfect circles, the distance between the sun and the moon and the earth is sometimes close and sometimes far away, so the shadow formed by the sunlight being blocked by the moon can be divided into the umbral shadow and the pseudo umbral shadow (the distance between the moon and the moon) on the earth. (formed when the Earth is farther away) and the penumbra. Observers can see a total solar eclipse within the umbral range; an annular solar eclipse can be seen within the pseudo-umbral range; and only a partial solar eclipse can be seen within the penumbral range. There are many mountains on the surface of the moon, and the edges of the moon are uneven. At the moment of eclipse or illumination, when the valley on the edge of the moon fails to completely block the sun, the unblocked part forms a luminous area, like a crystal "diamond"; the surrounding light red aperture forms the "ring" of a diamond ring. ”, overall, it looks like a diamond ring inlaid with bright gems. Sometimes many particularly bright rays or points of light are formed, as if a string of pearls are inlaid around the sun, called Bailey's beads (Bailey is a French astronomer).

[Edit this paragraph] Future prediction of solar eclipses

1: China has entered a period of high incidence of solar eclipses. There will be three solar eclipses in the next four years: China will usher in the first of this century Total eclipse the next day. In the next four years, the Chinese public will be able to enjoy three rare solar eclipses, one of which will be a total solar eclipse and two of which will be annular solar eclipses. Astronomical experts said that it is rare for so many solar eclipses to occur in five years. Zhao Zhiheng, director of the Tianjin Astronomical Society, said that since the 1980s, China has had two total solar eclipses that are conducive to observation. One was in Kunming, Guiyang and other southwestern cities in 1980; the other was in the Mohe area in 1997. . "The celestial phenomena of total solar eclipses this year and next, both in terms of the scope of the total eclipse zone and the time when the total eclipse occurs, will be conducive to observation by the Chinese public. As long as the weather is good, the public will be able to feast their eyes on it," said Zhao Zhiheng. In addition to the total solar eclipse on August 1 this year, an even more spectacular total solar eclipse will occur in China on July 22, 2009, with the total solar eclipse sweeping across the Yangtze River Basin in central China. By then, more than 40 cities in China, including Lhasa, Chengdu, and Shanghai, will be able to watch the total solar eclipse. Compared with the total solar eclipse on August 1, this total solar eclipse will occur in a wider range and last longer, lasting 5 to 6 minutes. This situation is a rare occurrence in a century.

In addition to these two total solar eclipses, an annular solar eclipse will also occur on January 15, 2010. The public in Yunnan, Sichuan, Hubei, Anhui and other places can see the annular solar eclipse. On May 21, 2012, an annular solar eclipse will be staged again, and the public in Guangxi, Guangdong, Fujian, Hong Kong and Macau can enjoy it.

2: 2008 solar eclipse forecast time and eclipse conditions in major cities across the country: On August 1 this year, a total solar eclipse will occur in China from Altay, Xinjiang, through Hami, Jiuquan, Xi'an and Zhengzhou. The starting time is It was around 18:20 Beijing time and lasted about two minutes. This is the first total solar eclipse to occur in China in the 21st century.

[Edit this paragraph] The number of occurrences

The following is the number of solar eclipses that occurred worldwide in the 20th century (1901-1999)

During this period, the sun Does not emit any special rays. Observations of solar eclipses are often misinterpreted. The Sun does not predict an eclipse on Earth and does not emit other rays, so there is no harm in staying outdoors during an eclipse. But when watching a partial solar eclipse, should you stare or take a quick glance? Although the sunlight during a solar eclipse is much weaker than usual, it is still harmful to the eyes if you look directly at it, and may damage the cornea. People stare or squint at the sun out of curiosity. Of course, a partial solar eclipse is still very dazzling. If you look at the sun for a long time, your cornea will be damaged before you know it. Eye damage during a solar eclipse is not due to abnormalities in the sun, but because people fail to pay attention to protective measures out of curiosity. Regardless of whether a solar eclipse occurs or not, do not look directly at the sun; do not use so-called "sunglasses"; do not use "sunglasses", even several stacked on top of each other; do not look at the image of the sun in mirrors or water; use size 14 Weld a mirror to view the sun; view with a specially coated Mylar mirror, which can be obtained from a famous planetarium or science museum; construct an aperture projector.

[Edit this paragraph] Misunderstandings about viewing the solar eclipse

Warning: It is a big misunderstanding to directly wear sunglasses (sunglasses) to observe the total solar eclipse. This is because the lenses have a focusing effect. If the sunglasses are too close to the eyes, the sun will burn the eyeballs, which may cause blindness in severe cases. It is not advisable to observe directly with the naked eye. The correct way is to take off the sunglasses at an arm's length from the eyes and observe the lenses from the side. In addition, it is also a good method to observe using the small hole imaging method or the basin reflection method.

You can also put a piece of glass coated with ink in front of your eyes, or put the glass on fireworks to blacken it. The thickness of the ink layer should be even so that your eyes can see the sun through it and turn it into a bronze color. , does not irritate the eyes and can be seen clearly. Never look directly at the sun with the naked eye or a telescope.

[Edit this paragraph] The story of the solar eclipse

For ancient people, solar eclipses were very scary. If you can understand the impact of the sun on food cultivation and daily life, you will be concerned about why the sun in the sky suddenly disappeared. In ancient China, a solar eclipse was believed to be caused by a dragon swallowing the sun. Other civilizations also considered it an ominous sign and had many "solutions": playing drums, shooting arrows into the sky, offering sacrifices of objects or people, etc. Rumor has it that there was once a fatal eclipse reporting error. This means that two Chinese astronomers in the second century BC did not report the solar eclipse for some reasons. At that time, the Chinese emperor believed that he was the emperor and attached great importance to celestial phenomena, believing that they were hints from God. Therefore, he invited a group of astronomers to observe the celestial phenomena regularly. Comets and meteors could not be predicted at that time, but solar eclipses were. The two astronomers did not tell the emperor about the occurrence of a major celestial event such as a solar eclipse. The emperor was furious and beheaded the two in public. Astronomers back then were much more dangerous than they are now.

Solar activity forecast

Changes in the environmental conditions of the sun and the earth are becoming increasingly important to modern cutting-edge technologies on which modern life and production depend. As mentioned earlier, X-ray flares directly cause disturbance in the earth's ionosphere, thereby affecting earth's shortwave communications. Solar proton events can endanger sensors and control equipment on astronauts and spacecraft, and also pose a radiation threat to passengers and crew flying in high latitudes. In addition, some statistics show that intense solar activity is related to earthquakes, volcanic eruptions, droughts and floods, heart and nervous system diseases, and traffic accidents. Therefore, solar activity and solar-terrestrial physics forecasts are very important. Solar activity forecasts are divided into long-term, medium-term, short-term forecasts and warnings. The solar-terrestrial space environment as a systematic scientific research object began in 1957 when humans entered space. The period from the 1950s to the 1970s was the exploration stage, and people gradually realized the importance of the space environment. Based on a large number of detections, a static model describing the environment was established, and safety predictions were made for some major aerospace activities. After the 1980s, driven by demand, research on the solar-terrestrial space environment has developed rapidly. The International Sun-Terrestrial Forecasting Conference, held every four years since 1979, has been held as scheduled, and its scale has been gradually expanded. In order to unite and coordinate the work of major countries, a joint forecast center was established. Headquartered in the United States, there are 10 regional alert centers located around the world. Our Beijing Regional Warning Center is one of them. After entering the 1990s, scientists vividly called it “space weather”.

Solar activity cycle

This cycle averages 22 years. It contains two 11-year sunspot cycles. In each cycle, the magnetic poles of sunspots are opposite in polarity. The changes of various other solar surface phenomena also have two high tides and two low tides like sunspots.

These solar phenomena include fluctuations in the frequency of solar prominences, flares, and magnetic effects, which include auroras and increased radio interference on Earth. The 11-year basic cycle of sunspots (sometimes called the solar cycle) was discovered by Schwabe in 1843. Some people try to link the solar activity cycle to changes in various other phenomena, such as small changes in the diameter of the sun. Even changes in tree rings are related to solar activity cycles.

How to estimate the time of a solar eclipse

The angle of view of the sun and the moon is about half a degree, and the moon revolution is 360 degrees, which means it moves half a degree every hour, that is, one moon position, so the solar eclipse takes up to 2 hours from start to end, that is, moving 2 positions of the moon. If it is not a total eclipse, the time will be shorter. In addition, because the earth is autorotating, the sun's position in the sky moves 15 degrees every hour. This means that within a range of 30 degrees, the sun and the moon move at the same time, and a solar eclipse occurs at the same time.

[Edit this paragraph] The earliest solar eclipse record

On May 26, 1217 BC, people living in Anyang, Henan Province, my country were engaged in various It was a normal activity, but something amazing happened. People looked up at the sky, and suddenly there was a gap in the radiant sun, and the light dimmed. However, after missing a large part, it began to recover again. This is the earliest record of a solar eclipse in human history. It is engraved on an oracle bone.

The observation of solar eclipses in ancient my country maintained the continuity of records. For example, the chronicle "Spring and Autumn" finally recorded 37 solar eclipses in 244 years from 770 BC to 476 BC. The recording of solar eclipses began in the 3rd century AD and continued into modern times for 1,600 to 700 years.

The longest solar eclipse

The longest solar eclipse (the moon is between the sun and the earth) lasts for 7 minutes and 31 seconds. The 1955 solar eclipse in West Philadelphia lasted 7 minutes and 8 seconds, the longest in recent history. It is predicted that a solar eclipse lasting 7 minutes and 29 seconds will occur in the mid-Atlantic region in 2186. A mother and child are photographed during a 1995 solar eclipse in Bangkok, Thailand, which was total in some parts of the country. The longest duration of a lunar eclipse (the Moon's movement into the Earth's shadow) is 1 hour and 47 minutes. On July 16, 2000, people saw this scene on the west coast of North America.

Since the orbits of the moon and the earth are not perfect circles, the distance between the sun and the moon and the earth is sometimes closer and sometimes farther away, so the shadow formed by the sunlight being blocked by the moon can be divided into the main shadow on the earth. , pseudo-umbra (formed when the moon is farther from the earth) and penumbra. Observers can see a total solar eclipse within the umbral range; an annular solar eclipse can be seen within the pseudo-umbral range; and only a partial solar eclipse can be seen within the penumbral range.