Why does the North Pole have a North Star and the South Pole not?

By a happy coincidence, half the planet is lucky enough to be able to look at a star that never moves from its place — when all the others change position.

The importance of the North Star, Polarisis so big that we use it as a metaphor for something that reliably guides us, and it is so memorable that some companies even bear its name.

In these times of GPS, its usefulness may have waned, but memories of its importance remain. However, there is no equivalent star at the South Pole, which raises the question: why not?

If we look up at the sky on a particular night and look again hours later, or at the same time on a different night, we will notice that the stars are moved — all except one. That is, if we are in the northern hemisphere.

If we are in the southern hemisphere, they will all appear to have moved. A long-exposure camera image will reveal the trails of the stars’ movements, all curved around a single point.

Of course, the stars themselves haven’t moved, at least not enough to tell at great distances without very precise instruments. Instead, it explains the, the Earth rotated, changing the location of the stars in relation to terrestrial objects, including the horizon.

Meanwhile, Polaris, at the tip of Ursa Minor’s tail, doesn’t seem to have movedat least to the naked eye.

The reason is simple: The Earth rotates on an axis, which points north and southfor points we call North and South Celestial Poles. The Earth’s rotation makes Polaris appear to revolve around the north celestial pole, and the two points are so close that the movement is imperceptible.

This, however, It’s pure coincidence. The universe was not made for usand Polaris’ proximity to the North Celestial Pole is just a matter of luck.

Already the southern hemisphere is not as lucky: there is no star, visible to the naked eye, that is aligned with the South Celestial Pole.

In dark skies, some people with excellent vision can distinguish Sigma Octantisjust over a degree from the South Celestial Pole, but distinguishing it from other faint stars is almost impossible, so it is very difficult to navigate with its help.

The exact distance a star must be from a Celestial Pole to be considered a pole star is decided arbitrarily, but whether a given star is less than 5 degrees will be seen as stationary.

Polaris, the brightest star in Ursa Minor, is less than 3/4 of a degree from the North Celestial Pole — which allows it to maintain its apparent position in the skies of the northern hemisphere.

For most of human history, it was difficult to find direction when traveling through unfamiliar territory. Even after the invention of crucial navigational instruments like the compass, sextant and astrolabe, these instruments were the privilege of a lucky few.

Thus, having a polar star to guide us was very important for the first navigators — thanks to a happy coincidence of points in the sky.