History
The classical zodiac was introduced in the neo-Babylonian period (ca. 7th to 6th century BC). At the time, the precession of the equinoxes had not been discovered. Classical Hellenistic astrology consequently developed without consideration of the effects of precession. The discovery of the precession of the equinoxes is attributed to Hipparchus, a Greek astronomer active in the later Hellenistic period (ca. 130 BCE).
Ptolemy writing some 250 years after Hipparchus was thus aware of the effects of precession. He opted for a definition of the zodiac based on the point of vernal equinox, i.e. the tropical system. While Ptolemy noted that Ophiuchus is in contact with the ecliptic, he was aware that the twelve signs were just conventional names for 30 degrees segments (especially since the Aries sign had ceased to be in contact with the Aries constellation already in his time).
The Hindu Jyotisha system opted for defining the zodiac based on the fixed stars, i.e. directly tied to the eponymous zodiacal constellations unlike Western astrological systems.
Read more about this topic: Sidereal And Tropical Astrology
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