The Lahiri ayanamsa is the angle between the tropical zodiac and the sidereal zodiac used in most Indian astrology. In 2026 it is about 24 degrees and 12 minutes.

If you have read sidereal vs tropical, you know the two zodiacs have drifted apart. This post is the practical follow-up: what the number is, where it comes from, and how to use it to find your own sidereal Sun.

What an ayanamsa is

"Ayanamsa" comes from Sanskrit words meaning roughly "movement" and "part". It is the number of degrees that the March equinox point has moved backward against the stars. Astrologers have proposed several values, because they anchor the zodiac to different reference stars or to different historical dates.

Lahiri is the most widely used one in India. It is named after Nirmal Chandra Lahiri, an astronomer who lived from 1906 to 1980. In its common form it fixes the star Spica near the start of the sidereal sign Libra. The value was about 23.84 degrees at the year 2000 and is about 24.2 degrees now. The Wikipedia article on ayanamsa lists the main systems side by side and notes that critics of Lahiri argue it is a little under what other methods give, which is a good reminder that this is a choice and not a law of nature.

It grows slowly

The value grows by about 50 arcseconds a year, the rate of axial precession. That is why it was roughly 23.85 degrees at the year 2000 and about 24.2 degrees now. Over a human life it grows by about one degree every 72 years, so your sidereal placements are very slightly different at different points in your life, but not enough to matter for a birth chart. If you want the physics behind the number, why the zodiac drifted covers it.

What it does to your Sun sign

To convert a tropical position to sidereal, subtract the ayanamsa from the tropical longitude. If your tropical Sun is at 10 degrees Aries, your sidereal Sun is about 24 degrees earlier, so at about 16 degrees Pisces. Only people whose tropical Sun is in the last six degrees or so of a sign keep the same sign. That is roughly one in five people. For everyone else the sidereal Sun is in the previous sign.

Roughly speaking, sidereal Sun signs start about 24 days later in the calendar than the tropical ones. Here is a rough guide to the dates:

  • Sidereal Aries begins around 14 April.
  • Sidereal Taurus begins around 15 May.
  • Sidereal Gemini begins around 15 June.
  • Sidereal Cancer begins around 16 July.
  • Sidereal Leo begins around 17 August.
  • Sidereal Virgo begins around 17 September.
  • Sidereal Libra begins around 17 October.
  • Sidereal Scorpio begins around 16 November.
  • Sidereal Sagittarius begins around 16 December.
  • Sidereal Capricorn begins around 14 January.
  • Sidereal Aquarius begins around 13 February.
  • Sidereal Pisces begins around 14 March.

These are approximate and can move by a day. Do not use them if you were born close to a boundary. Use a proper calculator and the exact time.

A Sun at 25 degrees of tropical Scorpio, around 17 November, is at about 1 degree of sidereal Scorpio, still in the same sign but only just.

Is "Sidereal 12" the same as Vedic?

They use the same zodiac and, usually, the same ayanamsa. Vedic astrology adds its own tools on top, such as the 27 nakshatras and the dasha timing system, and a different set of planets. The comparison is in Vedic vs Western astrology.

Why two calculators can disagree

Different tools use different ayanamsa values and different rounding, so your degrees may vary by a small amount. This matters most when a planet is close to a sign border. A difference of half a degree is enough to move a planet into the next sign.

If your Sun, Moon or rising sign is within a degree or two of a border, ask which ayanamsa the calculator used, and check the birth time. The Moon moves about 13 degrees a day, so an hour's error in your birth time can move it by more than half a degree.

A short checklist before you trust a chart

  1. Is the birth time accurate to the minute, or at least to a few minutes?
  2. Which ayanamsa was used (Lahiri, Raman, Krishnamurti)?
  3. Is the birth place converted to the correct time zone for that year? Time zones and daylight saving have changed a lot historically.
  4. Are you comparing like with like, sidereal with sidereal?

Find yours

The Solar Blueprint reading computes Sidereal 12 with the Lahiri value and shows your placements next to the tropical and 13-sign versions, so you can see the shift for every planet at once. I write each reading myself with my own engine and check it before you get it. For the background, see sidereal vs tropical, and if you have questions the ADHD MindFlow community is a good place to ask.

Astrology is a way to reflect, not science, and it does not predict events.

Astrology is a way to reflect, not science, and it does not predict events. Astronomy facts here are checked against the sources linked. Read our sources, commercial disclosure and editorial approach.