THE precession of the equinoxes - also known as Earth precession or "the big day” – is one of the many movements that the Earth performs. It occurs thanks to the fact that the Earth rotates in an inclined way, which causes that, every 25,770 years, it completes a revolution around the axis of its ecliptic. It gets this name because it has the ability to anticipate or precede the equinoxes (click here to find out what an equinox is).
As an example, the rotation of an unbalanced pawn is used, which, instead of rotating with the axis vertical, does so with the axis tilted, which allows its rotation to become “crooked”. Note the diagrams below:
Illustrative schematic showing, through a pawn, the precessional movement of the Earth
Illustration of the precession movement of the equinoxes. Compare it to the image above
The Earth's axis of inclination is 23.5°, a not very high value, which explains the fact that this movement is relatively slow, making it almost imperceptible to us. In one year, its movement is less than 1º of displacement. Despite this, it was discovered in Ancient Greece by Hipparchus of Alexandria, in the year 129 BC. C., through observations of changes in the position of the stars.
As we have already highlighted, precession causes an anticipation of the equinoxes - the moment in the movement of translation in which solar lighting is equally distributed in the two hemispheres terrestrial. Thus, each year, the equinoxes are brought forward 20 minutes, so that, every 2,000 years, we have a difference of one month.
From the point of view of the seasons, the changes are practically nil, but from the astronomical and even astrological point of view, the changes are considered relevant. That's because, currently, the equinoxes happen when the Sun is apparently positioned over the constellation of fish. However, in antiquity, it would have been positioned in the constellation of Aries.
This change in the constellation motivates a series of speculations about the so-called “big day”, because when the sun is positioned in the next constellation – Aquarius – we will have a new big day. This underlies a great deal of mythical and exoteric arguments, which pervade many religions. In the year 2150, the equinoxes will no longer happen in fish and will happen in Aquarius, motivating the belief that this will be a new period in human history, with the supposed presence of a "new Messiah".
Beliefs and myths aside, it is important to consider that the precession of the Equinoxes is just one of the countless movements that the Earth performs, which demonstrates that our planet, as well as the Solar System, the galaxies and the entire universe are in constant motion, in an eternal dynamicity.
By Rodolfo Alves Pena
Graduated in Geography
Source: Brazil School - https://brasilescola.uol.com.br/geografia/precessao-dos-equinocios.htm