Zodiac

The Zodiac, or “circle of animals” is an area or belt in space projected onto the celestial sphere through which, from our point of view, the planets move. A symbolic geometric construction from 15 to 18 degrees in width, is divided into 12 signs, each of 30 degrees of longitude (making 360 degrees in all), with the ecliptic, the apparent path of the Sun, as its mid-line.

The tropical zodiac defines the spring point (the first day of spring in the northern hemisphere) as the first degree of Aries, but the sidereal zodiac allows it to precession. Many people are confused about the difference between the sidereal zodiac and the tropical zodiac signs. Because of an “oscillation” in the rotation axis of the Earth for a period of about 26,000 years (often called “big year”), the speed at which the spring equinox precesses in the skies is about 0 degrees, 0 minutes , 50.23 seconds a year, adrift of one degree every 72 years.

The precession of the equinoxes takes place at a rate of about 5 arc-minutes every six years. Tropical signs refer to the seasons and not to the stars. Here is an example: a person born, say August 28, 2002, would come to understand that his Sun sign was in Virgo according to Western astrology (traditional solar sign from August 23 to September 22 of each year), but the sun in that same calendar date of the year 2002 was in the constellation of Leo (where it had been since 10 August 2002 and would remain until September 15, when he would then finally enter the Virgin).

It is worth stressing that the sidereal signs and the tropical signs are both geometric conventions of 30 ° each, while the zodiacal constellations are pictorial representations of mythological figures projected on the celestial sphere based on patterns of visible groupings of stars, none of which occupies precisely 30 ° ecliptic. So constellations and signs are not the same thing, even if for historical reasons they could have the same names