The ancient Beidou once had nine stars. Why is it now seven?

The Big Dipper, most people also know its location. These seven stars make up one? Spoon? This shape, so people often call it the Big Dipper? Spoon star? What's it called? Beidou? Is it because it is the same as the ancient wine set? Fight? It is very similar in shape and always appears in the night sky in the north, so it is also called the Big Dipper. This one? Spoon? Or? Fight? The two stars at the front end are Polaris, and the distance is five times that of the straight line extending forward.

The Big Dipper revolves around the North Star once a year. In spring, summer, autumn and winter, bucket handle points to the southeast and northwest respectively. The ancients discovered this phenomenon long ago, so they also used the position of the Big Dipper to judge the season. Since ancient times, the Big Dipper has been the most familiar star. Thousands of years ago, the big dipper that the ancients saw was very different from what we see now. The nine planets of Beidou? Because there seemed to be nine stars in the position of the Big Dipper at that time, the ancients in China said that the Big Dipper was composed of Shu Tian (greedy wolf), Tian Xuan (giant gate), Tianji (Lucun), Tian Quan (Wen Qu), Yuheng (Lian Zhen), Kaiyang (Wu Qu) and Yaoguang (Pojun) in Ziwei Garden. Besides these seven stars, there are two stars on the handle of the Big Dipper, namely Zuo Fu and Youbi. ?

Zuo Fu and Youbi were still bright thousands of years ago, but then the light gradually dimmed, and the luminosity was much weaker than the other seven stars, so they were no longer considered as the nine planets of the Big Dipper, and gradually changed to the Big Dipper. ?

It is generally believed that the luminosity of Zuofu and Youbi stars may have changed greatly due to the activities of some stars. For example, they once had helium flash, so their luminosity will be very bright at first, but it will gradually dim over time, and now it is difficult for the naked eye to see.