Understanding the Sidereal Zodiac
Jyotish uses a different methodology than what we have come to know as Western astrology today. Although these two systems both track the planets along their ecliptic path through the 12 classical constellations, each use a different reference point to begin their map of the heavens. These two maps are referred to as the Sidereal Zodiac utilized in Jyotish, and the Tropical Zodiac employed in Western astrology.
The Tropical zodiac describes 0° Aries as the position of the Sun at the Vernal equinox, regardless of the part of the zodiac it’s observed to be in. The Sidereal Zodiac aligns the beginning of its zodiac by the position of the bright, brilliant marker star Citrā, at exactly 0° Libra, which is 180° across the zodiac from 0° Aries. Oriented to this marker star, the sidereal zodiac maintains a fixed and unchanging map of the heavens. By contrast, the Tropical zodiac drifts away from the observable positions of the sky in a slowly widening gap of about one degree every 72 years. Dubbed “the procession of the equinoxes”, this phenomena is due to the wobble of the earth as it rotates upon its axis. This causes the vernal equinox to drift incrementally through the zodiac year after year. This moving gap between Sidereal 0° Aries and the vernal equinox equated with 0° Aries in the Tropical system is known as the ayanāṃśa. This translates to a 24° disparity between Sidereal and Tropical Zodiacs in their placement of the planets along the ecliptic.
The last time that the vernal equinox coincided with the Sun’s placement at 0° Aries was approximately 285 BCE. At present the Sun transits roughly 6° Pieces on the first day of spring, as observable in the sky. It take twenty-three thousand years before the vernal equinox occurs at 0° Aries again and the earth complex one full “wobble”, fulfilling one full rotation of the equinox points around the ecliptic plane.
I hope this short and digestible description of the Sidereal Zodiac will serve as has a helpful introduction to this topic and serve as a gateway to further understand this beautiful science of light.
