In both historical astronomy and astrology, the zodiac is a circle of twelve divisions of 30° each of the celestial longitude. These divisions are centered on the ecliptic, which is the apparent path across the heavenly sphere the Sun takes over the year, and are referred to as the zodiac signs. The paths followed by the moon and other visible planets equally remain close to this ecliptic inside the 3rd house astrology. This belt extends between eight and nine degrees (celestial latitude) to the south or north of the ecliptic.
In essence, the zodiac is a coordinate system celestial of celestial bodies, or, to be more specific, an ecliptic coordinate system using the ecliptic for the latitude’s origin, and the sun’s position at vernal equinox for the latitude’s origin. It is of importance to distinguish the zodiac signs from their associated constellations, partly because a precession of equinoxes causes them to drift apart, and partly because the varying forms and shapes of these physical constellations take up different widths (in degrees) of the ecliptic.
The constellation of Virgo, for example, takes up five times as much of the ecliptic longitude as the constellation of Scorpius. The zodiac signs represent an abstraction of the physical constellations and are designed to represent the longitude the Sun traverses in around 30.4 days, which is exactly 30°, or one twelfth of the full 360° circle each. These twelve divisions are used as the primary reference frame in calculating – from a geocentric view point – the positions of varying celestial bodies.
It would, for example, be possible to find the sun in 19° Aries (19° longitude), or the moon in 25° Cancer (115° longitude. Jupiter may be found to be in 14° Leo (134° longitude) at some point in time. As these numbers indicate, Aries is the first of the zodiac signs, occupying 0 – 29° of the celestial circle. This is followed by Taurus at 30 – 59°, Gemini at 60 – 89° and Cancer from 90 – 119°. Leo resides at 120 – 149°, with Virgo following on at 150 – 179°, Libra extending from 180 – 209° and Scorpio occupying 210 to 239°. Sagittarius begins at 240° and ends at 269°, with Capricorn (270 – 299°), Aquarius (300 – 329°) and Pisces (330 – 359°) completing the circle.
Representing the ram, bull, twins, and crab; the lion, maiden, scales and scorpion; the archer (or centaur), goat, water bearer, and fish respectively, each of the twelve zodiac signs is believed to indicate specific characteristics and experiences. These characteristics of the individual zodiac signs, the positions of varying planets and other points, such as the Ascendant and Midheaven, the cusps of the astrological houses and the Vertex – all of which depend on an individual’s location and the time of their birth – are taken into consideration when a personal horoscope or birth chart are prepared.