What are the classic jokes in astronomy?

One of the largest sauropods found in China, a fossil was found at Mamingxi Ferry in Yibin City, which was scientifically identified as sauropods. This animal is about 22 meters in length and nearly 14 meters in height. Its neck is extremely long, equivalent to half of its body length, which not only constitutes the length of each cervical vertebra of the neck, but also has as many as 19 cervical vertebrae, making it the most one of sauropods. In addition, the neck rib is also the longest among all dinosaurs (the longest neck rib can reach 12.438+0 meters). Compared with cervical vertebra, there are relatively few vertebrae, sacrum and coccyx.

Mamen Xilong lived about 6,543.8 billion years ago. Mamenxilong was almost invisible at that time, indicating that the apparent magnitude of this star was 9.49 1 100 million years ago. One hundred million years later, people can hardly see it. At this time, the apparent magnitude of this star is 6. The smaller the apparent magnitude, the brighter the star.

Thinking: Mamenxilong and human beings are different creatures, and the brightness of the stars will be different. Mainly the difference in pupil diameter (which can be considered as equivalent to the telescope aperture). Mamenxilong was almost invisible 1 100 million years ago, but we can hardly see it today (extreme magnitude), which shows that the apparent brightness of stars changed between 1 100 million years. Assuming that the distance between the star and the earth is constant, the limit magnitude of Mamenxilong can be known according to the pupil diameter (M= 1.77+5lgD). Then we must estimate the pupil diameter of Mamenxilong. Knowing the extreme magnitude of Mamenxilong and human beings, we can know that this star has changed its apparent magnitude several times in 654.38 billion years. Then infer what kind of star it is.

People can hardly see it with the naked eye (apparent magnitude is 6). According to M= 1.77+5lg D(M is the limit magnitude of a telescope with a diameter of d), the pupil diameter of a person can be calculated, and D=7mm can be obtained. Then estimate the pupil diameter of Mamenxilong.