The solar system moves 7 billion kilometers every year, but the North Star is always due north. Why is this?

In our universe, whether it is as big as a galaxy or as small as an electron, it is always in motion, even when we think we are sitting still in a chair, the earth is carrying us at every second The speed of about 30 kilometers revolves around the sun, and the sun is also moving, in fact, it is orbiting the center of the galaxy with the entire solar system, and the speed is as high as about 220 kilometers per second.

A simple calculation shows that the solar system moves about 7 billion kilometers per year. What is puzzling is that the solar system is always moving, but the North Star we see is always due north. Why is this?

If we walk in an environment with a wide field of vision and observe a distant scene, then we will find that although we have walked a certain distance, in our eyes, the distant scene does not appear relative to our position what changes. In general, the further away the scene is from us, or the shorter the distance we move, the more pronounced this phenomenon is.

Now let’s take a look at Polaris. Observational data show that the distance between Polaris and us is about 433 light-years, which is about 4 trillion kilometers. It can be seen that the 7 billion kilometers that the solar system moves every year is not much compared to this distance. Worth mentioning.

In terms of the ratio between the two, it is as if a scene is 5.7 kilometers away from us, and we only move 1 cm per year. At such a speed, even if we move for 10,000 years, it is difficult to observe it. The relative position to us has changed.

In the vast cosmic space, the speed of the solar system can be said to be slower than that of a snail. Only after a long period of time will the relative position of the Polaris seen on the earth change significantly. In other words, the North Star is not always in the true north, but only temporarily in the true north. As long as the time is long, it will leave the true north sooner or later.

Then the question arises, if one day the North Star leaves due north, will the people on earth still call it the North Star?

Of course not, because the North Star actually refers to "the star closest to the north celestial pole", which we can simply understand as the star pointed to by the north end of the Earth's rotation axis is the North Star.

That is to say, the North Star is not a special name for a certain star, but is held by different stars in turn. When the star we call North Star leaves the true north, the people of the earth will rotate the earth again. The other star to which the north end of the axis points is called Polaris.

It should be noted that the rotation axis of the earth is not as unchanged as we imagined. According to the observations of astronomers, the rotation axis of the earth will periodically swing under the gravitational action of the sun and the moon, which is probably like this. .

This is called "Earth precession," which has a period of about 25,700 years, and will change the name Polaris more rapidly than the solar system's motion of 7 billion kilometers per year. So which star will the "next" North Star be? Let's see.

The current North Star is "Gou Chenyi", also known as "Alpha Ursa Minor", and its current position in the sky is constantly approaching the North Celestial Pole, and will reach the nearest position in the next few decades, after this , it will drift away from the northern celestial pole, and in about 500 years, the closest to the northern celestial pole will be a star named "Gouchen Si".

"Gou Chensi", also known as "Xi Minor" (pronounced "Kexi"), has an apparent magnitude of 4.28, which is far less bright in the night sky than "Gou Chenyi" with an apparent magnitude of 1.98. ", it will not be the North Star for too long. In 3300 AD, the North Star will be served by "Shaowei Zengba", and in 4400 AD, the North Star will be held by "Shaowei Zengqi" ...

summary

In short, we earthlings refer to the star that lies due north as the North Star, and once the star leaves due north, it is no longer the North Star. And the reason why we think that the North Star is always due north is because for us humans, the name of the North Star has been changed for too long.