Concepts in Astronomy #15. Axial Precession

Axial Precession

The axial precession period of a celestial object (in this case Earth) is the movement that the Earth's axis does changing its orientation slowly and progressively, completing a whole circle in 25772 years. This movement is like the one of a spinning-top, with the axis creating two cones joined at their apices.

If there were no axial precession, the location of the stars in the celestial sphere (described by the Equatorial Coordinate System), would be almost invariable and not moving slowly through the years as it actually does.

For example, the star Polaris (dec +89°20'37" is currently very close to the North Celestial Pole (+90°). In a few thousand years another star would be closer and it will take 25772 years for Polaris to repeat its same position as today in the Celestial Sphere.

Another effect is the gradual change of the position of the Sun in relation to the background constellations of the ecliptic at the time of the equinoxes. Currently, at the time of the the March Equinox, the Sun is in the region of Pisces. In a few hundred years, it will be in the region of Aquarius.

1000px-Earth_precession.svg.png

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Credits

- Galaxy image obtained from Pixabay under CC0. No Copyright. The person who associated a work with this deed has dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law

Concepts in Astronomy #15. Axial Precession

Axial Precession

Credits

- Precession image obtained from NASA.gov. No Copyright.