The term zodiac is usually used to refer to a division of the ecliptic into segments that are thought to be endowed with certain qualities and meanings in astrology.
Zodiac in Western Astrology
The term is most commonly used in western astrology to refer to the division of the ecliptic into twelve 30-degree segments known as “signs.”
The western zodiac was originally developed and standardized so that it consisted of 12 segments consisting of 30 degrees each by the 5th century BCE in Mesopotamia. It became widely adopted by other cultures in subsequent centuries after the development of horoscopic astrology.
Zodiac as a General Term
The term zodiac has also come to have a more generalized meaning, so that sometimes the term is used in order to refer to other divisions of the ecliptic into specific segments, even if they differ from the western 12 sign zodiac.
For example, the Indian system of 27 lunar mansions known as the nakshatras is sometimes referred to as a lunar “zodiac”, since it divides the ecliptic into specific segments.
Similarly, the Chinese have a 12 sign “zodiac” that divides the ecliptic into 12 sections as well, although these sections are associated with entire years rather than individual months, and the qualities associated with each segment are different than in the western zodiac.
Determining whether the term “zodiac” is being used to refer to the western system of dividing the ecliptic into 12 segments, or whether it is being used more generally in order to refer to some other system of dividing the ecliptic into segments, will depend on the context in which the term is used.
Different Methods of Calculating the Western Zodiac
It should also be noted that there is some disagreement amongst those who use the western zodiac as to where the starting point should be, and what the zodiac represents as a reference system.
Those who use the tropical zodiac use the vernal point as the starting point, which is the first degree of Aries, and thus they use the equinoxes and the solstices as the primary reference points for their zodiac.
On the other hand, those who use the sidereal zodiac tend to use the constellations that lie along the ecliptic as the primary reference point for their system, although there is some disagreement about the precise degree that should be used as the starting point.