In astrology, the zodiac is based on the division into twelve equal parts of the celestial band on which the trajectories trace the Sun, the Moon, and the planets, advancing one sector for each month of the year. Each sector contains the traditional constellation to which it owes its name. The Babylonians and Greeks divided this band into twelve equal parts, each of them being a sector of the sky of an extension of thirty degrees of arc, baptized with the name of the twelve most outstanding constellations that they saw in each of the subdivisions. The zodiac has a fundamental importance in Western astrology. Other cultures with an astrological tradition such as China also attach special importance to this region of the sky, although they define a different zodiac.
In astrology the constellations of the zodiac define the twelve zodiacal signs. Zone or celestial strip through whose center passes the elliptical orbit that describes the Earth in its movement around the Sun and that contains the twelve constellations or signs.
Actually the zodiac of astrology is not composed of the zodiacal constellations but by the astrological signs that make up the so-called horoscope. The constellations of the zodiac are the groups of stars cut by the plane of the orbit of the Earth projected in the interstellar space, and the signs are archetypes (in the memory) with which the astrologers define the personality of the people and are associated to 12 astrological months of about 30 days of the calendar year. Those 12 months form the astrological year, and its first day coincides with the spring or vernal equinox in the Northern Hemisphere, when the Sun is at the beginning of the constellation of Pisces, and hence in astronomy is spoken of the Pisces Pointer. While, astrologically, it is the 1st day of the first month / sign (Aries) of the astrological year, and that is why in astrology we speak about the Pointer of Aries. Both pointers are the same concept although with different names, one astronomical and the other astrological. The Indian, Persian and Bahá'í cultures also begin their year at the vernal equinox. In the Gregorian calendar the 1st of Aries corresponds to March 21, and as the astrological dates are dated according to the Gregorian form, hence each astrological month is dated in Gregorian format from about the 21st of a Gregorian month to more or less the 21 of the following month. But the months and their astrological signs do not correspond to the length of the zodiacal constellations, and while the number of the months / signs is 12, that of zodiacal constellations is 13 with Ophiuchus, which is an astrological sign but not of the horoscope. The only thing that the constellations of the zodiac and astrological signs of the horoscope have in common is the names, but that does not mean they are the same.
