If there is a magpie bridge, how many magpies do you need to build it？

"Look at the blue sky on Tanabata tonight, and lead the cowherd and weaver girl to cross the river bridge". On August 22nd, the seventh day of the seventh lunar month, Chinese Valentine’s Day was ushered in, which is also the legendary day when the Cowherd and the Weaver Girl meet at the Yinhe Magpie Bridge once a year. Then, the question is, if there is a magpie bridge, how many magpies will it take to build it?

The Milky Way that people see with the naked eye is actually a part of the Milky Way, which is composed of a large number of stars. In ancient times, it was also called Tianhan, Xinghan, Tianhe and Jianghe. According to legend, the Magpie Bridge is built on this Tianhe River.

Xiu Lipeng, a member of the Chinese Astronomical Society and an expert in astronomical science, said that there are three bright stars near the Milky Way-Vega in Lyra, Altair in Aquila and Tianjin IV in Cygnus, which constitute the symbol of the summer starry sky-"Summer Triangle".

Lu Shupei, a fan of Beijing astrophotography, photographed the Milky Way and the "Summer Triangle" in Sangendalai Town, Zhenglan Banner, Xilin Gol League, Inner Mongolia on July 30, 2017. (Photo courtesy of myself)

In the Han Dynasty, Cowherd and Weaver Girl were completely anthropomorphic. "All the way to the Altair, Jiaojiao River Han female … Ying Ying Yi Shui, the pulse can not be said." In Chinese fairy tales, it is said that the Cowherd and the Weaver Girl are separated from each other. Only at the seventh day of the seventh lunar month every year, the magpies in the sky build a magpie bridge to connect the two sides of the Milky Way, and the lovers of the Cowherd and the Weaver Girl can meet.

Dai Jianfeng, a fan of astrophotography in Chongqing, and Wang Xiaomo, a painter, jointly filmed the "Cowherd and Weaver Girl Galaxy Bridge Club". (Photo courtesy of myself)

Theoretically, it is very difficult for the Cowherd and the Weaver Girl to "meet". According to modern astronomical observation and calculation results, the distance between Altair and Vega is about 16 light years, and 1 light year is about 9.46 trillion kilometers. Even if Altair calls Vega, Vega will not hear it until about 16 years later.

"Such a long distance, if you really need to use magpies to build a magpie bridge, it can be described as’ a huge project’. The average length of magpies is about 45 cm. According to the calculation, the distance between Altair and Vega is 16 light years multiplied by 9.46 trillion kilometers, divided by the average body length of magpies, which is about 3.36356 billion. It takes at least 3.3 billion magpies to build a magpie bridge before the Cowherd can be sent to Vega. This also shows that the annual meeting between the Cowherd and the Weaver Girl on the Qixi Bridge is just a kind and beautiful wish of people. " Xiu Lipeng said.

Original title: "If there is a magpie bridge, how many magpies do you need to build it? 》

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