Are east, west, south and north fixed?

The four basic directions of east, west, south and north are the most basic common sense. Everyone knows them since childhood. In some places, even when giving directions on the street, people will say east, west, south and north. But do you know how these four directions are determined?

You may say, what's so difficult about this? East is the direction where the sun rises, west is the direction where the sun sets, south is the direction of the compass, and north is the direction of the North Star.

Indeed, the ancients probably divided the directions into east, south, west and north in this way. However, there are actually very big problems with this.

Why? Because these four things are actually subject to change.

Let's talk about the sun first. Although we all say that the sun rises from the east, if you observe carefully, you will find that the direction of the sun's rise changes with the seasons. For example, in most parts of China, the sun rises from the northeast in June and July, and becomes the southeast in November and December.

The same is true when it sets. If the sun rises from the north-east, it will set from the north-west. If it rises from the south-east, it will set from the south-west.

Something that is always changing cannot be used as a strict standard. Therefore, we can say that the sun rises roughly from the east, but we cannot say that the direction it rises is due east.

So what to do? Actually, there are two days every year when the sun does rise due east and sets due west. You may already be familiar with these two days, namely the spring and autumn equinoxes. So, a better definition of east is "the direction where the sun rises during the spring and autumn equinoxes", and west is "the direction where the sun sets during the spring and autumn equinoxes". The closer you are to the spring and autumn equinoxes, the more the sun conforms to the east-west direction; the farther you are from the spring and autumn equinoxes, the further the sun deviates.

What about the compass? It actually does not point to the geographic south or north, but to the Earth's north and south magnetic poles. These two magnetic poles, one near the North Pole and the other near the South Pole, do not coincide with the true North Pole and South Pole. Moreover, these two magnetic poles are still drifting, and the drift speed has accelerated in recent years.

Therefore, the compass only points to the "approximate" south, not the strict south.

As for the North Star, it is indeed almost above the North Pole, but it is still not accurate, there is still a little difference. Moreover, the position of the stars relative to the earth will also change. The current North Star will not be the North Star in a thousand years.

A better definition of north and south is to use the axis that the Earth rotates on. Imagine that the Earth rotates around a pole, and the intersection of the pole and the Earth's surface is the South Pole and the North Pole, and due south and due north are the directions to the South Pole and the North Pole, respectively.

Now you know that the methods we usually use to judge the directions are not accurate and will change over time. The deviations of the compass and the North Star are relatively small, while the deviations of the rising and setting of the sun are sometimes very small and sometimes very large. Of course, in daily life, we don't need to be very precise, but if we want to drive a boat, fly a plane or go to the wild, then pursuing precision is very important.