Zodiac 30° along the ecliptic is nominally designated as the zodiac sign Aries, which no longer falls within the proximity of the constellation Aries since the effect of precession is to move the vernal point through the backdrop of visible constellations (it is currently located near the end of the constellation Pisces, having been within that constellation since the 2nd century AD). The subsequent 30° of the ecliptic is nominally designated the zodiac sign Taurus, and so on through the twelve signs of the zodiac so that each occupies 1/12th (30°) of the zodiac's great circle. Zodiac signs have never been
Zodiac is sometimes assumed. Ptolemy also demonstrates that the principle of the tropical zodiac was well known to his predecessors within his astrological text, the "Tetrabiblos", where he explains why it would be an error to associate the regularly spaced signs of the seasonally aligned zodiac with the irregular boundaries of the visible constellations: Astronomically, the zodiac defines a belt of space extending 9° either side of the ecliptic, within which the orbits of the Moon and the principal planets remain. It is a feature of a celestial coordinate system centered upon the ecliptic, (the plane of the Earth's orbit and