Will the Big Dipper cease to exist in the future?

Foreword

The stars are shining brightly, the sky is returning to the Big Dipper, the midsummer moon is full, and the weeds are growing in the sky. How many children’s first sight of the Big Dipper stars happened on such a night?

"Move the small stool and stand by the window again, and learn about the Big Dipper in the sky."

The Big Dipper is one of the most easily recognized constellations. It consists of seven stars located in the northern hemisphere sky and is shaped like an ancient wine scoop. The body of the bucket consists of four stars, which was called "Kui" in ancient times; the handle of the bucket consists of three stars, which was called "Lao" in ancient times. Now is the summer when the days are long and the nights are short. When the stars first appear at night, the Big Dipper always appears high in the sky to the right of the sunset.

Figure 1: The Big Dipper

The Big Dipper is most famous for finding Polaris - the star pointing to the North Pole of the Earth to point the direction. The North Star is in (almost) the same place in the sky, motionless, and the other stars revolve around it. Thus, finding the North Star determines which direction is north. The North Star can be found by connecting the first two stars of the Big Dipper's body and extending it about 5 times toward the mouth of the Dipper. The Beidou satellite navigation system independently developed by our country also follows this meaning. In ancient times, the Beidou satellite identified the direction, and today the Beidou satellite locates Kyushu.

Picture 2: The Big Dipper and the Polar Star

There are also "bears" in the night sky

In our country, the Big Dipper from the body to the handle is called "Tianshu, Tianxuan, Tianjin" , Tianquan, Yuheng, Kaiyang, Yaoguang (Yaoguang)". Tianshu, Tianxuan, Tianji, and Tianquan form the fighting body, while Yuheng, Kaiyang, and Yaoguang form the handle. In ancient times, the Seven Stars of the Big Dipper were also called " Greedy Wolf, Jumen, Lucun, Wenqu, Lianzhen, Wuqu, and Pojun".

Picture 3: The name of the Big Dipper

In the Western constellation system, the Big Dipper is part of the Ursa Major and is the tail of the "bear". The seven stars from the body to the handle are named Ursa Major α, Ursa Major β, Ursa Major γ, Ursa Major δ, Ursa Major ε, Ursa Major ζ, and Ursa Major eta.

Figure 4: Ursa Major

Interestingly, the constellation where the North Star is located - Ursa Minor, looks very much like the Big Dipper, and is sometimes called the "Little Dipper". The end of the bucket handle is now the North Star.

Picture 5: Ursa Minor (Little Big Dipper)

Unfortunately, such a wonderful Big Dipper will eventually lose to the years and no longer have the shape of a "dipper". To find out the reason, we need to understand the past and present lives of the Big Dipper.

The past and future of the Big Dipper

Generally speaking, stars in the same constellation often just look like "neighbors", but in fact they are likely to be far apart. Miraculously, the stars in the Big Dipper have a very close "kinship". Except for Tianshu and Fluctuating Light, which are located at both ends of the Beidou, the other five stars are more than 80 light-years away from us, which shows that their actual distances (in an astronomical sense) are also relatively close! In addition, in 1869, British astronomer Richard Proctor discovered that the five stars of the Beidou were moving in almost the same direction and at almost the same speed. It can be seen that they are not only close to each other, but also have an extraordinary relationship.

In 1960, American astronomer Orin Egan proposed the concept of Moving Star Groups, which refers to a series of stars of similar age, similar chemical composition, similar distance and movement. The five stars in the Beidou belong to the moving star group closest to the solar system - the "Ursa Major Moving Group".

Figure 6: Part of the Ursa Major Moving Star Group

How is the Ursa Major Moving Star Group formed? Why do these stars have so many similarities? Based on calculations of star lifetimes, astronomers believe that the Ursa Major Mobile Group was once an open star cluster , formed in a primitive nebula about 500 million years ago. Nebula is composed of cosmic dust, hydrogen, helium, etc. Their collective motion, gravity, magnetic field, etc. maintain a delicate balance. This balance is easily disrupted by external disturbances (such as supernova explosions), leading to large density inhomogeneities in certain areas of the nebula. Due to the influence of gravity, some of these dense places began to gather and collapse, eventually forming a series of stars. In other words, these stars are all "brothers" born in the same nebula, have the same formation reasons, and are born at very similar times; their chemical composition and motion are inherited from the nebula, so they are also very similar.

Figure 7: Omega Nebula

These stars are relatively close to each other. They can be bound to each other by gravity to form a star group, referred to as "星cluster". Among them, Open Star Cluster is a type of loosely organized star cluster. The famous Pleiades and Hyades clusters in Taurus belong to open star clusters. The stars in this cluster are not particularly close, and their mutual gravitational pull is weak. The gravitational pull of the nebula or other star clusters can easily cause the members to break away from the organization and no longer bind each other, but they still maintain similar movement directions and speeds. At this point, the open cluster collapsed and became a moving cluster.

Figure 8: Pleiades star cluster

It can be seen that there are only five stars in the Big Dipper They are true "brothers", but Tianshu and Yaoguang have different origins from them and are not "of the same mind". The movement direction of Tianshu and Fluctuating Light is almost opposite to that of the other five stars, so in the distant future, with the movement of the seven stars, the shape of Beidou will change—— 天曰 Chuan After passing the extension line connecting Tianxuan and Tianji, the shape of "dou" will no longer exist , and the description of "Beidou hanging with beads hanging upside down" is no longer applicable. However, for the creatures on the earth, this process takes a long time, about one hundred thousand years, so you don’t have to worry too much~

Figure 9: Future changes in the Big Dipper

Postscript

For thousands of years, some patterns in the sky have always been Being observed and deified.

A variety of celestial objects can be seen in the night sky: famous planets, sparse nebulae, distant galaxies, as well as ephemeral visitors such as comets and meteors.

With its unique shape and important role in determining direction, the Big Dipper has been valued and praised since ancient times. In legends and astrology, the Big Dipper has become a representative symbol of the laws of nature and the order of heaven and earth, bringing people unlimited imagination. Even today, the names of the Big Dipper can often be seen in film and television works and games, which shows its far-reaching influence. ; In astronomy, the Big Dipper has provided indispensable help for humans to explore the universe and study star formation, star clusters, star groups, etc.

The summer night sky is filled with stars and clouds; the story of Xingya is filled with sands in the Ganges River. If you encounter a leisurely long night, please look up!

The sky is open to everyone. It is right next to you, but it represents an extremely distant time and space. Looking up is such a simple act, but it can awaken our deepest imagination, and at the same time make us meditate.

——"Stargazing with the Naked Eye"

This article comes from the WeChat public account: WeChat public account (ID: null), author: Xilong

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