Sidereal vs Tropical: Why Your Vedic Sign Is Different

Many people who look up their Vedic chart for the first time find that their Sun sign is not the one they grew up with. A Western Leo is often a Vedic Cancer. Neither is wrong: the two traditions measure the zodiac from different starting points.

Two zodiacs

The tropical zodiac of Western astrology begins at the spring equinox — the point where the Sun crosses the celestial equator around 21 March — and calls that point 0 degrees Aries, whatever stars lie behind it. The sidereal zodiac of Jyotish is fixed to the stars themselves; the nakshatras and signs keep their place against the background constellations.

Precession

The two zodiacs drift apart because the Earth’s axis slowly wobbles like a spinning top, a motion called the precession of the equinoxes. The equinox point moves backwards through the stars by about 50 seconds of arc a year — one degree every 72 years, a full circle in about 25,800 years. The two zodiacs coincided around the 3rd to 5th century CE; today they differ by just over 24 degrees.

The ayanamsa

The difference between the two zodiacs on a given date is the ayanamsa. A Vedic chart is calculated by finding each planet’s tropical position and subtracting the ayanamsa. Several ayanamsas exist, differing by when exactly the zodiacs are taken to have coincided. The most widely used in India is the Lahiri, or Chitrapaksha, ayanamsa, which places the star Spica (Chitra) at 0 degrees Libra. It was adopted in 1955 by the Calendar Reform Committee of the Government of India and is used in the official national ephemeris. Others include Raman and Krishnamurti (KP), which differ from Lahiri by a fraction of a degree to about a degree and a half.

What it changes

• Planets in the first 24 degrees or so of a tropical sign move back one sign in the Vedic chart.
• The Lagna and the houses shift with them.
• Nakshatras are only defined in the sidereal zodiac, so the nakshatra, Dasha and Guna Milan all depend on it.
• Transit dates such as Saturn’s entry into a sign, and therefore Sade Sati, are sidereal dates.

Which one is right?

They are different systems, each internally consistent. Western astrology is built on the seasons; Jyotish is built on the stars and the Moon’s nakshatras. What matters is not mixing them: a Vedic reading uses sidereal positions throughout, and a tropical Sun sign cannot be used to look up a Vedic horoscope.

VedicsAstro uses the Lahiri ayanamsa for every chart. Your Kundli shows each planet’s sidereal sign and degree, along with its nakshatra and pada.