The formation of solar and lunar eclipses
Introduction to solar eclipse
A solar eclipse is when the moon revolves around the earth and rotates between the sun and the earth. If the sun, moon, and earth are exactly aligned or close to a straight line, the moon blocks it. When the sun's rays hit the earth and the dark shadow behind the moon falls on the earth, a solar eclipse occurs. 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. 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 close and sometimes far 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.
When a total solar eclipse occurs, it can be divided into five types of eclipses based on the positional relationship between the lunar surface and the sun's spherical surface: 1. First loss. The moon moves faster than the apparent motion of the sun. The moon catches up with the sun during a solar eclipse. When the eastern edge of the moon just "contacts" with the western edge of the sun, it is called the first waning, which is the first "exocution" and the beginning of the solar eclipse; 2. Eat. About an hour after the initial waning, the moment when the eastern edge of the moon and the eastern edge of the sun are "inscribed" is called an eclipse, which is the beginning of a total solar eclipse. At this time, the moon covers the entire sun; 3. Eat very much. It is the moment when the sun is most eclipsed, and the center of the moon moves closest to the center of the sun; 4. Generate light. The moment when the western edge of the moon and the western edge of the sun are "in-cut" is called photogenesis, which is the end of a total solar eclipse. It usually only takes two or three minutes from eclipse to photogenesis, and the longest is no more than seven and a half minutes; 5. Round. About an hour after the onset of light, when the western edge of the moon "touches" the eastern edge of the sun, it is called a complex circle. From this time on, the moon completely "separates" from the sun, and the solar eclipse ends.
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.
Picture Caption
Picture Caption: How did part of the sun disappear? This is the part of the sun that happens to be hiding behind the moon at that time. This was the first partial solar eclipse of 2005 and the last total solar eclipse observable until March 2006. During a solar eclipse, the sun, moon and earth are in a straight line. This total solar eclipse first appeared in the South Pacific, and the area where the partial eclipse can be observed spans South America and North America to the south. The scene above was captured with a handheld digital camera last Friday. After a whole day of rain in the Holly Mountains of North Carolina, the United States, the partially eaten sun temporarily broke through the dark clouds in the sky. After taking a series of images, the best photo of the eclipse was digitally combined with a less good photo that showed an airplane.
Number of occurrences
The following is the number of solar eclipses that occurred worldwide during the 20th century (1901-1999):
Partial eclipses 78
Annular solar eclipse 73
Total solar eclipse 71
Mixed eclipse 6
Total 228
The process of lunar eclipse
The penumbral eclipse begins after a total lunar eclipse: the moon has just come into contact with the penumbral area and is not noticeable to the naked eye at this time.
The formal process of a lunar eclipse is divided into five stages: initial waning, complete eclipse, extreme eclipse, light generation, and full circle.
First waning:
Marks the beginning of the lunar eclipse. The moon slowly enters the earth's shadow from its eastern edge, and the moon and the earth's umbra are circumscribed for the first time.
Eclipse:
The western edge of the moon is inscribed with the western edge of the earth's umbra, and the moon just completely enters the earth's umbra.
Eclipse:
The center of the Moon is closest to the center of the Earth's umbral shadow.
Light generation:
The eastern edge of the moon is inscribed with the eastern edge of the Earth's umbra, and the total eclipse phase ends.
Compound circle:
The western edge of the moon is extrinsic to the eastern edge of the Earth's umbral shadow. At this time, the entire lunar eclipse ends.
The degree of eclipse of the moon is called "eclipse fraction", which is equal to the ratio of the farthest distance from the edge of the moon wheel deep into the earth's umbra to the apparent longitude of the moon at the time of the eclipse.
End of penumbral eclipse: The moon leaves the penumbral shadow, and the entire lunar eclipse process officially ends.
Knowledge about watching solar eclipse
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During this period, the sun will 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 a mirror or water;
Look at the Sun with a No. 14 welded mirror; look with a specially coated Mylar mirror, which can be obtained from a famous planetarium or science museum; construct an aperture projector.
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.
Appendix
Related knowledge about the sun
Solar prominence
Solar prominence is a solar activity phenomenon that protrudes outside the edge of the sun. When a solar prominence appears, the chromatic sphere in the atmosphere resembles a burning grassland, and the rose-red tongue-shaped gas rises like a fire. It has various shapes, some are like floating clouds, some are like arch bridges, some are like fountains, and some are like clumps of grass. , some are as beautiful as holiday fireworks, and overall their shape is just like earrings attached to the edge of the sun, hence the name "solar prominences". The rising height of a solar prominence is about tens of thousands of kilometers. Large solar prominences can be hundreds of thousands of kilometers above the sun. They are generally about 200,000 kilometers long, and some can reach 1.5 million kilometers. The brightness of the solar prominence is much dimmer than the solar photosphere, so it cannot be observed with the naked eye at ordinary times. It can only be seen directly during a total solar eclipse. Solar prominence is a very peculiar solar activity phenomenon. Its temperature is between 5000 and 8000K. Most of the solar prominence materials slowly fall to the sun after rising to a certain height, but there are also some solar prominence materials floating in the sun with temperatures as high as 2 million K. The lower layer of the corona neither attaches nor disintegrates. It is as strange as a piece of ice that does not melt in a blazing steel-making furnace. Moreover, the density of the prominence material is 1,000 to 10,000 times higher than that of the corona. The two are actually the same. It is really puzzling that it can be stored for several months.
Corona
The outermost atmosphere of the sun is called the corona. The corona extends from several to dozens of times the diameter of the sun. During solar maximum years, the corona is nearly circular; during solar quiet years, it is elliptical.
b] There are large irregular dark areas in the corona, called coronal holes. A coronal hole is a region of lower gas density in the corona. There are three types of coronal holes: polar coronal holes, isolated coronal holes, and extended coronal holes. Solar energy loses matter in the form of the solar wind -- a stream of matter particles. Coronal holes are an important source of high-speed solar wind. A coronal mass ejection is a very macroscopic and huge material and magnetic field structure that occurs in the corona. It is a sudden explosion of large-scale dense plasma. Nothing has the greatest impact on the planet.
When there are strong explosions and coronal mass ejections on the sun, the powerful plasma flow carried by the solar wind may reach the Earth's polar regions. At this time, auroras appear at both poles of the earth. The forms of the auroras are ever-changing. Auroras also occur on some planets in the solar system that have magnetic fields. Flares that occur in the corona are called X-ray flares, and their wavelengths are only 1 to 8 Angstroms or shorter. It directly causes disturbance in the earth's ionosphere, thereby affecting earth's shortwave communications.
Sun wave
A type of ejection phenomenon of material in the solar photosphere. It usually occurs over sunspots and has a strong ability to reappear. When a surf falls along the ascending path, it will trigger a new surf to rise into the sky. This repeats, but its scale and height are smaller each time. , until it disappears. The surf at the edge of the sun appears as a small, bright hummock with a sharp spike-shaped top that grows outward. The height of ascent varies from person to person. A small wave can only reach a few hundred kilometers, a large wave can reach 5,000 kilometers, and the largest one can reach 10,000 to 20,000 kilometers. The maximum ejection speed can reach 100-200 kilometers per second, which is more than 100 times faster than the fastest reconnaissance aircraft. When they reach their highest point, they begin to fall under the influence of the sun's gravity until they return to the sun's surface. People have discovered from high-resolution observational data that surfing is composed of a very small bundle of fibers. The distance between each fiber is very small, and they shine and move together as a whole.
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.
The earliest solar eclipse record
On May 26, 1217 BC, people living in Anyang, Henan Province, my country were engaged in various normal activities, but one day 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 a total solar eclipse in some parts of the country. The maximum 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.
Ten-year solar eclipse timetable
Best observation points for year, month and day types
2008 2 7 Antarctica, Pacific Ocean
2008 8 1 All of Canada, Arctic Ocean, Soviet Union, China
2009 1 26 All of Atlantic Ocean, Indian Ocean, Indonesia
2009 7 22 All of India, China, Pacific Ocean
2010 1 15 Around Africa, Indian Ocean, Myanmar, China
2010 7 12 All over the Pacific, southern South America
2012 5 21 Around China, Japan, Pacific Ocean, United States
2012 11 14 All Australia, Pacific Ocean
2013 5 10 Around Australia, Irian Island, Pacific Ocean
2013 11 3 All Around Atlantic Ocean, Africa
2014 4 29 Rim of Antarctica
2015 3 20 All of the Atlantic Ocean, Spitsbergen Islands, and the Arctic Ocean
2016 3 9 All of Indonesia and the Pacific Ocean
2016 9 1 Rim Atlantic Ocean, Africa, Indian Ocean
2017 2 26 Pacific Rim, southern South America, Atlantic Ocean, southern Africa
2017 8 22 All Pacific Ocean, United States, Atlantic Ocean
2019 7 3 All Pacific, South America
2019 12 26 Rim of Arabia, India, Indonesia, Pacific
2020 6 21 Rim of Africa, Arabian Peninsula, Pakistan, China, Pacific
2020 12 15 All Pacific, southern South America, Atlantic Ocean
2021 6 10 Rim of northeastern North America, Arctic Ocean, Soviet Union
2021 12 4 All Atlantic, Antarctica, Pacific< /p>
2023 4 20 The entire circumference of the Indian Ocean, Irian Island, and the Pacific Ocean
2023 10 15 The circumference of the Pacific Ocean, southern North America, northern South America, and the Atlantic Ocean
2024 4 9 All Pacific, southern North America, Atlantic Ocean
2024 10 3 Pacific Rim, extreme southern South America, Atlantic Ocean
2026 2 17 Rim Antarctica, Indian Ocean
2026 8 13 All Arctic Ocean, Greenland, Atlantic Ocean, extreme western Europe
2027 2 6 Pacific Rim, extreme southern South America, Atlantic Ocean
2027 8 2 All Atlantic Ocean, extreme northern Africa, extreme Asia Southwest, Indian Ocean
2028 1 26 Pacific Rim, northern South America, Atlantic Ocean, western Europe
2028 7 22 All Indian Ocean, Australia, Pacific