If you've just looked up your rising sign in Vedic astrology and found that it isn't the sign you've used for years, nothing is broken. Indian astrology calls the Ascendant the lagna, and it measures it against a different zodiac. Once you see how the two zodiacs line up, you can usually predict your Vedic Ascendant from your Western one in a few seconds.
Two zodiacs, one sky
Western astrology uses the tropical zodiac, which starts at the spring equinox, the moment the Sun crosses the celestial equator in March. Vedic astrology uses a sidereal zodiac, anchored to the background stars. Because the Earth's axis wobbles very slowly, the two have drifted apart over many centuries. Right now the gap, called the ayanamsa, is a little over 24 degrees under the widely used Lahiri system.
Your tropical Ascendant comes from the Rising Sign calculator. To estimate the sidereal one, subtract about 24 degrees.
The quick rule for your rising sign in Vedic astrology
- If your Western Ascendant is past about 24° of its sign, your Vedic lagna is most likely the same sign.
- If it is below about 24°, your Vedic lagna is most likely the sign before.
So a Western Ascendant of 10° Gemini becomes roughly 16° Taurus in a Vedic chart. A Western Ascendant of 27° Gemini stays in Gemini, at about 3°. Close to the 24° line, check the exact ayanamsa your Vedic source uses, since Raman, Krishnamurti, and others differ slightly from Lahiri.
Which one is my real Ascendant?
Both, within their own systems. Neither is a correction of the other. Each tradition has its own rules for reading the lagna, its ruler, and the houses, and those rules were built around its own zodiac. Mixing them, say reading a sidereal lagna with Western sign descriptions, tends to produce muddled results.
My suggestion is to pick the tradition you want to learn and stay consistent within it. If you're reading Western material, use the tropical Ascendant. If you're working with a Jyotish astrologer, use the lagna they give you.
In Jyotish the ruler of the lagna, the lagna lord, carries a lot of weight, just as the chart ruler does in Western work. Since your lagna may move back one sign, the ruling planet can change as well. A Western Gemini Ascendant has Mercury as its ruler, but if the Vedic lagna is Taurus, Venus takes that role instead, and the reading follows Venus through the houses.
Charts drawn differently, too
Vedic charts are often drawn as squares rather than wheels. In the North Indian style the lagna is always the top central diamond, with a number showing its sign. In the South Indian style the signs stay in fixed boxes, and the lagna box is marked with a diagonal line or the letters ‘La’ or ‘Asc’.
For the Western side of the story, including chart rulers and houses, see Astrology Geeks.