Ayanamsa choices

Ayanamsa

The ayanamsa is the correction that converts a tropical zodiac position into a sidereal zodiac position. It's a single number — usually 23-24° in our era — that gets subtracted from every tropical longitude to give you the corresponding sidereal longitude. The choice of ayanamsa only matters if you've switched to the sidereal zodiac. In tropical work, the ayanamsa is irrelevant — there's no offset to apply.

If you've never touched the zodiac system knob, you don't need to think about ayanamsa. If you're switching schools to Vedic Classical, the ayanamsa decides where every planet lands.

Why an ayanamsa exists at all

The tropical zodiac is locked to the seasons — 0° Aries always sits at the vernal equinox. The sidereal zodiac is locked to the fixed stars — 0° Aries was originally placed at a chosen star reference point. Because of precession, the equinox slowly drifts backward against the stars at about 1° per 72 years. The two zodiacs are always offsetting from each other.

The ayanamsa tells you, for a given date, how far apart the two are. To get a sidereal position, you take the tropical position and subtract the ayanamsa.

The trick is that "the fixed stars" don't define a unique starting point — you have to pick one. Different traditions pick different stars and call the result by different names.

Lahiri (Chitrapaksha)

The official ayanamsa of the Indian government and the Vedic astrological mainstream. Defined so that the star Spica (Sanskrit: Chitra) sits at exactly 180° in the sidereal zodiac — i.e., at 0° of sidereal Libra, exactly opposite the sidereal 0° Aries.

This is the ayanamsa the modern Vedic canon was standardised against in the 1950s by the Indian Calendar Reform Committee. Virtually all contemporary Jyotish practice — the major Indian publishers, software, and teachers — uses Lahiri. Currently about 24°10'.

If you're working in Vedic Classical, Lahiri is almost certainly the right choice. The interpretive material was written assuming Lahiri positions.

Krishnamurti (KP)

A refinement of Lahiri used in the Krishnamurti Paddhati (KP) system — a 20th-century South Indian innovation that subdivides the nakshatras further (into sub-lords and sub-sub-lords) for precise prediction work. The KP ayanamsa is calibrated about 5-6 arc-minutes tighter than Lahiri, which sounds tiny but can matter when you're working at sub-degree precision.

Outside KP work, this ayanamsa is rarely used. If you're not specifically doing KP-style prediction, Lahiri is the right default.

Fagan-Bradley

The Western sidereal standard. Cyril Fagan and Donald Bradley developed it in the 1940s-50s as part of their attempt to bring Western astrology back into a sidereal frame. It's calibrated using a different stellar reference set than Lahiri — based on Spica at 29° sidereal Virgo rather than 0° sidereal Libra. The result is about 50 arc-minutes (just under 1°) of difference from Lahiri.

Fagan-Bradley is the standard for Western sidereal practitioners. If you've intentionally chosen to read Western astrology in a sidereal frame — a deliberate choice, since Western tradition has been tropical since the Hellenistic synthesis — this is the conventional ayanamsa.

How much do the choices differ?

50 arc-minutes is almost a full degree. That's small enough that no planet will shift by a sign — sign placements are stable across the three ayanamsas. But it's large enough that a planet sitting near a house cusp could land in different houses, especially in unequal house systems. Aspect orbs are also slightly affected.

When the ayanamsa knob does nothing

The ayanamsa knob is silently inactive when the zodiac system is tropical. There's no offset to apply if you're using the seasonal zodiac directly. StarBind will compute a Lahiri or Krishnamurti or Fagan-Bradley value internally for use by some routines (for example, calculating nakshatras even in a tropical chart, if you ever want them as supplementary data), but your displayed planet positions are unaffected by the ayanamsa choice.

If you switch the zodiac to sidereal and the ayanamsa is still set to its default, the calculator just uses that default. You'll only see the ayanamsa choice matter in the chart positions when both knobs (zodiac = sidereal AND a non-default ayanamsa) are set.

Practical guidance

• Vedic Classical: Lahiri. No good reason to pick anything else unless you're explicitly doing KP work.
• KP-style prediction: Krishnamurti. The system was built around it.
• Western sidereal: Fagan-Bradley. The English-language sidereal material assumes it.

In all three cases, the choice of ayanamsa matters far less than the choice of zodiac system itself. The 50 arc-minute differences between ayanamsas are dwarfed by the 24° difference between tropical and sidereal as a whole.