Why have the Big Dipper remained together for thousands of years and not fallen apart?

This is a question raised by a friend. He couldn't figure it out for a long time. Now that he has figured it out, he may feel better.

It's not that the Big Dipper is strung together, but that all the stars in the sky are strung together. If this friend knew this "shocking secret", would he be even more confused?

Humans have recorded history for thousands of years, and the stars in the sky have always been the same, with basically no change. That's why stars are called "eternal" stars. Eternal means long-lasting, everyone understands this, right?

The stars whose positions change quickly are called "planets". The "planet" in "planet" means moving. Everyone understands this, right?

In ancient times, people did not know the "secrets" of these stars and believed that the stars in the sky were all gods. Therefore, the moving stars were the great gods, patrolling and inspecting work everywhere, while the motionless stars were just on guard and their role was certainly not as great as that of the moving stars.

Therefore, people pay special attention to those stars that move and change faster, thinking that their abilities and positions must be greater and higher than those that do not move. For example, the five stars of gold, wood, water, fire and earth have become the five most important stars in people's lives. The so-called Yin and Yang and Five Elements, with infinite changes, and mutual generation and mutual restraint, refer to these five stars.

We now know that the stars that move are actually planets that are very close to us. These planets are insignificant compared to stars, with masses only hundreds of thousands to millions of times that of stars, while the largest stars are hundreds of millions of times the mass of the Earth.

But these planets are very close to us, only tens of millions to billions of kilometers away. They only move within the solar system and orbit the sun. Since each planet is in its own orbit, the speed of movement varies. Therefore, when observed from the earth, they are in different positions throughout the year or even in different years.

There are only five planets that we can see with our naked eyes, namely Mercury, Venus, Mercury, Fire and Saturn. The farthest of these planets is Saturn, which varies between 1277340000-1576540000km as it moves with the Earth.

Generally, the distance between celestial bodies in the solar system is measured in astronomical units. 1 astronomical unit (AU) is about 150 million kilometers. So the farthest planet we can see with our naked eyes, Saturn, is about 8.5~10.5 AU away from us, with an average of about 9.5 AU. The distance between celestial bodies outside the solar system is calculated in light years. 1 light year is about 9.46 trillion kilometers, or about 63067 AU.

If Saturn is calculated in light years, it is only about 1/6638 light years away from us.

The distance between stars and us is completely different. The nearest star is several light years away. The nearest star to us is Star C in the Centauri A triple star system, also known as Proxima Centauri, which is 4.22 light years away from us. The mass of this star is only about 1/8 of the sun, but it is more than 40,000 times the mass of the earth, and it can emit light, but because it is too far away, we cannot see it with our naked eyes.

Therefore, the nearest star we can see is Star A in Centaurus A, which has a mass 1.1 times that of the Sun and is about 4.3 light years away from us. Therefore, stars are very far away from us, so although stars move very fast, compared with the distance, measured by the human eye, they are slower than a snail.

This is why the Big Dipper has always been shaped like a spoon. It was shaped like this in ancient times, and it is still shaped like this today. Because the composition of the stars is somewhat strange and they are relatively bright, they aroused great interest and imagination in ancient people. At that time, people could not figure out what the sun, moon and stars were, so they anthropomorphized them and regarded them as important stars to predict the fortunes and misfortunes of life.

In the famous story of the Three Kingdoms, Zhuge Liang worshipped the Big Dipper. However, he did not receive the protection of the Big Dipper in the end, and died of illness due to overwork. Although the book describes that the worship failed because Wei Yan's intrusion blew out the Seven Stars, in fact, there is no necessary connection between the two. If the real Zhuge Liang in history gained his fame by relying on such supernatural talk, it would be the greatest sorrow.

The seven stars of the Big Dipper, from Big Dipper One to Big Dipper Seven, start from the front end of the dipper body to the tail of the handle, in order, are named: α, β, γ, δ, ε, ζ, η in Greek; and their Chinese names are: Tianshu, Tianxuan, Tianji, Tianquan, Yuheng, Kaiyang, and Yaoguang.

Among these stars, the brightest is Yuheng, one of the Big Dipper's five stars, whose brightness is almost close to first magnitude; Tianquan, one of the Big Dipper's four stars, is the dimmest and is a third magnitude star; the other five are all second magnitude stars.

There is actually no relationship between these seven stars, but they just look like this from the perspective of our earth. Like all stars, these stars are also moving, and the direction of movement is not uniform. Some are approaching us, some are moving away from us, and some are moving sideways.

Moreover, the speed of star movement is often tens or even hundreds of kilometers per second. For example, our sun, along with celestial bodies of all sizes in the solar system, moves around the center of the Milky Way at a speed of about 250 kilometers per second.

But why can't we see the changes of the Big Dipper? This is because they are too far away from us, and they are also too far away from each other, tens of light years or even hundreds of light years away. In fact, the Big Dipper is only an object of worship for the Chinese. In the international constellation classification, it is only a part of the Ursa Major.

The farthest of the Big Dipper is the first star on the mouth of the Big Dipper, about 124 light years away; the closest star is the second to last star on the tail of the Big Dipper, about 78.2 light years away. The rest are between 80 and 101 light years away.

Let's think about it. Even if one of these stars moves horizontally at a speed of 100 km per second, it will take 3,000 years to travel 1 light year. If the distance between two stars in the Big Dipper is 100 light years, then the distance has changed by 0.33% in 1,000 years. Can we see it with our naked eyes?

In fact, it is relatively rare for stars to completely move away from each other from our perspective. For example, Tianxuan, Yaoguang, and Yuheng are all approaching us, with apparent velocities of 12km, 11km, and 9.3km per second, respectively, which makes it even harder to see.

This is why the stars appear to change little over thousands of years.

Of course, modern scientific and technological means can measure this change, and even smaller changes can be measured, but the human eye cannot see it.

But after tens of thousands of years, we can see its changes. According to the apparent velocity of the Big Dipper, through computer modeling, 100,000 years ago, the mouth of the Big Dipper was more like a diamond-shaped arrow, and 100,000 years later, it was more like an excavator bucket with a broken handle. (See the picture above)

That’s it, welcome to discuss, thanks for reading.

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