Zodiac
The zodiac is the name of the belt surrounding the apparent path the Sun follows across the sky through the year. In astronomy it is a region of the sky; in astrology it is a symbolic system divided into twelve equal signs. The two uses share a word but do not describe the same thing.
| In brief | The zodiac is the belt extending around the Sun's apparent path across the sky, within which the Moon and the planets also appear. |
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| Astronomical account | The zodiac is the belt of sky extending about 8 to 9 degrees on either side of the ecliptic; 13 constellations, with boundaries defined by the International Astronomical Union, cross this belt, and the Sun appears in each of them for a different length of time. |
| Use in astrology | The tropical branch of Western astrology divides the zodiac into 12 equal signs of 30 degrees each, beginning at the vernal equinox, and interprets planetary positions according to these slices. Indian astrology, by contrast, uses the sidereal zodiac, which is aligned to the stars. |
| Evidence status | The zodiac belt and the constellation boundaries are astronomical realities confirmed by observation. Whether the sign slices relate to personality or to events, however, has not been demonstrated in controlled studies; this layer of interpretation is a cultural and symbolic tradition rather than a scientific one. |
| Common misconceptions |
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A belt across the sky
As the Earth travels around the Sun, the Sun appears to us to shift slowly in front of the stars. The belt extending about 8 to 9 degrees above and below this apparent path, the ecliptic, is called the zodiac. Because their orbital planes lie close to one another, the Moon and the planets always appear within this belt or near it; the zodiac is for this reason the lane of the sky along which the traffic flows.
Two different ways of dividing
Astronomy divides this belt by constellation boundaries: 13 constellations cross the belt, Ophiuchus included, and their sizes differ greatly. The common branch of Western astrology, by contrast, divides the belt into 12 equal slices of 30 degrees each, starting from the vernal equinox; these slices are the signs, and they take their names from the constellations of antiquity. Because of precession, these slices no longer coincide with the constellations of the same name.
Why is it still confused?
Using the same names, Aries, Taurus, Gemini and so on, for both the constellations and the signs creates the impression that the two systems are one and the same. Yet one is a region on the physical map of the sky and the other a symbolic slice of a coordinate system. Knowing this distinction lets you follow both sky observation and debates about astrology more soundly.
Related terms: The Ecliptic, Constellation, Precession, Sun Sign