...of the Earth's Rotation Axis



The Earth's rotation axis is not fixed in space.


Like a rotating toy top, the direction of the rotation axis executes a slow precession with a period of 26,000 years (right figure).


Pole Stars are Transient

Thus, Polaris will not always be the Pole Star or North Star.


The Earth's rotation axis happens to be pointing almost exactly at Polaris now, but in 13,000 years the precession of the rotation axis will mean that the bright star Vega in the constellation Lyra will be approximately at the North Celestial Pole, while in 26,000 more years Polaris will once again be the Pole Star.



Precession of the Equinoxes


Since the rotation axis is precessing in space, the orientation of the Celestial Equator also precesses with the same period.


This means that the position of the equinoxes is changing slowly with respect to the background stars.

This precession of the equinoxes means that the right ascension and declination of objects changes very slowly over a 26,000 year period.


This effect is negligibly small for casual observing, but is an important correction for precise observations.



The Dawning of the Age of Aquarius (Almost)

Because of the precession of the equinoxes, the vernal equinox (see left figure) moves through all the constellations of the Zodiac over the 26,000 year precession period.


Presently the vernal equinox is in the constellation Pisces and is slowly approaching Aquarius.


Since the point where the projection of the rotation axis of the Earth strikes the Celestial Sphere moves around (the stars are still not in motion), this means that the North Celestial Pole moves around through the stars.


This produces changes in the coordinates of stars (even though they are not moving). Today, it is fortuitous that the North star is Polaris (see right figure).


At other times, other stars will be the North star.