The Earth in its orbit around the Sun causes the Sun to appear on the celestial sphere moving along the ecliptic (red), which is tilted 23.44° with respect to the celestial equator (blue-white).

The zodiac is an area of the sky that extends approximately 8° north or south (as measured in celestial latitude) of the ecliptic, the apparent path of the Sun across the celestial sphere over the course of the year. The paths of the Moon and visible planets are also within the belt of the zodiac.[1]

In Western astrology, and formerly astronomy, the zodiac is divided into twelve signs, each occupying 30° of celestial longitude and roughly corresponding to the constellations: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces.[2][3]

These astrological signs form a celestial coordinate system, or even more specifically an ecliptic coordinate system, which takes the ecliptic as the origin of latitude and the Sun's position at vernal equinox as the origin of longitude.[4]

  1. ^ "zodiac". Oxford Dictionaries. Oxford University Press. Retrieved 19 September 2017.
  2. ^ Because the signs are each 30° in longitude but constellations have irregular shapes, and because of precession, they do not correspond exactly to the boundaries of the constellations after which they are named.
  3. ^ Noble, William (1902), "Papers communicated to the Association. The Signs of the Zodiac.", Journal of the British Astronomical Association, 12: 242–244, Bibcode:1902JBAA...12..242N
  4. ^ Leadbetter, Charles (1742), A Compleat System of Astronomy, J. Wilcox, London, p. 94; numerous examples of this notation appear throughout the book.