Vedic Astrology is Star Based or Sidereal — Western is Season Based or Tropical
It is important to know that Vedic astrological calculations are different from what most of us have seen in the Western systems. Vedic Astrology is sidereal or based in reference to the stars. All its calculations are constantly adjusted for a back slipping motion of the earth called precession. The earth\’s axial spin retards or moves back about one degree or one day every 72 years, in relationship to a fixed star. The astronomy of the sky that you observe each night in our modern times is nearly matched to the zodiac constellations used in Vedic Astrology calculations.
In Western astrology, the planetary positions presented in their Zodiac do not represent today\’s astronomical positions. They tend to focus more on the seasons as markers of time. The Tropical zodiac remains unchanged from what was seen in the skies almost 2000 years ago by the ancient Greeks, Egyptians and Babylonians. The two systems are about 23 days apart (called the \”ayanamsa\”) from where they mark the first point of the sign of Aries, which is the start of the circle of the zodiac (you have to start a circle somewhere). Again, this is due to that slow precessed, backward slipping of the earth. What this means, astrologically, that unless you were born somewhere between the 15th and 20th of the month, your Sun sign will most likely move back one sign in Vedic Astrology.