1. The coordinate system which measures Celestial Longitude eastward along the Ecliptic, beginning with the Vernal Point, and measures Celestial Latitude along great circles perpendicular to the Ecliptic. In this system, Tropical Aries begins at the Vernal Point. Also called the Hipparchus Tropical Zodiac.
2. No less than five Tropical Zodiacs existed during the Greco-Roman period. Each placed the Vernal Point in various degrees of their respective `sign' of Aries: ARI 15?° - Eudoxus of Cnidus ARI 12?° - Cleostratus of Tenedos ARI 10?° - Naburiannu ARI 08?° - Kidinnu (Greek: Cidenas) ARI 00?° - Hipparchus (and Ptolemy) By far, the most popular of these was that of Kidinnu (ARI 08?°). The value used by Hipparchus (ARI 00?°), which has become the modern Tropical Zodiac, was prefered only by Posidonius, Geminus (his pupil), and Claudius Ptolemy. The confusion which existed among the Greeks on these assignments is clear from their written accounts, and demonstrates their lack of knowledge of more ancient Egyptian and Babylonian astrology. ---or A coordinate system which rotates with respect to the stars. Named for the Tropics of Cancer and Capricorn. Longitude is measured from the Vernal Point, which moves westward among the stars at a rate of about 1?° each 72 years. No less than 5 Tropical Zodiacs were used by Greek astrologers.