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Zodiac denotes an annual cycle of twelve stations or "signs" along the ecliptic, the apparent path of the Sun across the heavens, dividing the ecliptic into twelve equal zones of celestial longitude. As such, the zodiac is a celestial coordinate system, more precisely an ecliptic coordinate system, taking the ecliptic as the origin of latitude, and the position of the sun at vernal equinox as the origin of longitude.
It is known to have been in use by the Roman era, based on concepts inherited by Hellenistic astronomy from Babylonian astronomy of the Chaldean period (mid 1st millennium BC), which in turn derived from an earlier system of lists of stars along the ecliptic. The construction of the zodiac is described in Ptolemy's Almagest (2nd century AD).
The term zodiac may also refer to the region of the celestial sphere encompassing the paths of the Moon and the naked eye planets (Mercury, Venus, Mars, Jupiter, and Saturn), corresponding to the band of about eight arc degrees above and below the ecliptic. The zodiac of a given planet is the band which contains the path of that particular body, e.g. the "zodiac of the Moon" is the band of five degrees above and below the ecliptic. By extension, the "zodiac of the comets" may refer to the band encompassing most short-period comets