DIFFERENTS POLE STARS
I- Past , present, future
1) Past
The polar star used to be another star of the constellation from the polar star, Beta Ursa Minoris or Kochab (which means " pole star " in Arabic). It is a star without any particular characteristics, it hasn't got anything special in its past.
2) Present
Currently the pole star is polaris Alpha Ursae Minoris. It enables the locating of the north.
3) Future
In 2102 it will be 27'30'' away from the north pole. Then it will drift away towards. In 7600 the new polar star will be Alderdmin (Alpha Cepheus) then in 14000 it was Vega (Alpha of the Lyre).
II- Presentation of the pole stars
1) In the past
For less than 10000 years, there has been two pole stars before polaris :
- tau Hercule about less than 8000 years.
- alpha Dragon about less than 3000 years.
Before the invention of the GPS, it was difficult to find one's bearings at sea. Only the pole star could help the navigators to locate themselves. Indeed the pole star is nearly on the rotation axis of the earth (about 1° ). But you had to be in the northern hemisphere.
At the time when a lot of Christians went to Jerusalem, people had to find how to find their way. To reach this aim, an Irish bishop (Nicolas) proposed a method which used the pole star again. It consists in lying on the horizontal ground, feet in the north direction. If we put the right fist on the right knee and, if the pole star is exactly with above the thumb, it means we arrived to the Jerusalem latitude.
2) In the future
- Around 7600, it will be Alderamin from the constellation of Cepheus (alpha of Cepheus).
- Around 14000, it will be Vega from the constellation of the Lyre (alpha of the Lyre).
Click on the image to see great format.
III- Precession equinox
The precession equinox is extremely slow because a complete cycle lasts 26,000 years. The precession of the axis of rotation of the earth leads to the drifting of the position of the celestial poles.
Of this way, stars wich show the north pole change on a period of 26,000 years. This results into a change in the position of the celestial equator. The equinoxes also drift according to that cycle because they correspond to the intersection of the celestial equator and the elliptic. That's why we called this phenomenon the precession of the equinoxes