Lahiri ayanamsa: the gap that turns the tropical zodiac into the sidereal one

What is the ayanamsa?

The word comes from the Sanskrit ayana, the course (here, that of the equinoxes and solstices), and amsha, the portion. The ayanamsa is the arc travelled by the spring equinox point since the time when the two zodiacs coincided. In other words, the distance between 0° tropical Aries, set on the equinox, and 0° sidereal Aries, tied to the stars.

The conversion rule fits on one line: sidereal position = tropical position − ayanamsa. A tropical Mars at 5° Gemini, minus 24°13′, gives a sidereal Mars at 10°47′ Taurus. Every position moves back by the same amount, planets, Ascendant and Midheaven included: that is why your Sun and your Ascendant often change sign, as the tropical vs sidereal comparison explains.

The precession of the equinoxes: why the ayanamsa grows every year

The Earth’s axis slowly traces a circle in the sky, like a wobbling spinning top, and completes one turn in almost 26,000 years. This is the precession of the equinoxes: the spring equinox point slips back against the stars by about 50 seconds of arc a year, or one degree in roughly 72 years, and a whole sign in a little over two thousand years.

So the ayanamsa grows by the same amount every year. According to the Lahiri calculation, it was zero around the year 285, when the two zodiacs lay on top of each other. A few milestones:

• 1950: about 23°10′.
• 1985: about 23°39′.
• 2000: about 23°51′.
• 2026: about 24°13′.

For a birth chart, what counts is the ayanamsa on the day of birth, not today’s: between a birth in 1960 and one in 2020, there is already a gap of about 50′.

The Lahiri ayanamsa (Chitrapaksha), India’s official reference

It is named after N. C. Lahiri, a Bengali astronomer and member of the Calendar Reform Committee set up by the Indian government in the early 1950s and chaired by the physicist Meghnad Saha. In 1955, the committee adopted his calculation to unify the country’s calendars. It has been used for India’s official ephemerides ever since, and it is the ayanamsa of the vast majority of Vedic astrologers.

Its other name, Chitrapaksha, means “on the side of Chitra”. Chitra, “the bright one”, is the Sanskrit name for Spica, the brightest star in the constellation Virgo. The Lahiri calculation fixes it at 0° sidereal Libra, exactly 180° from 0° Aries. Spica thus falls at the exact middle of the nakshatra that bears its name, Chitra, from 23°20′ Virgo to 6°40′ Libra.

Why this star? Because it is bright, easy to find, and lies about two degrees from the ecliptic, the path of the planets: an ideal marker for tying the zodiac to the sky of the stars.

Raman, Krishnamurti, Fagan-Bradley: the other ayanamsas

Sidereal astrologers all agree on precession, but not on the exact date when the two zodiacs coincided. Each school therefore has its own ayanamsa, a few minutes or more than a degree away from Lahiri. The best known:

• Raman: put forward by B. V. Raman, a widely read Indian astrologer of the 20th century. It is about 1°27′ smaller than Lahiri: a planet in the last degree and a half of a sign according to Lahiri moves into the next sign.
• Krishnamurti: the one used in KP (Krishnamurti Paddhati, “the method of Krishnamurti”), devised by K. S. Krishnamurti to read very fine subdivisions of the nakshatras. It is only about 6′ smaller than Lahiri.
• Fagan-Bradley: the one used in Western sidereal astrology, founded in the mid-20th century by the Irishman Cyril Fagan and the American Donald Bradley. It is a little less than one degree larger than Lahiri.

If you compare your Vedic chart from one program to another, check the chosen ayanamsa first: most differences come from there, not from how the planets are calculated.

Mean or true ayanamsa: the site’s choice

Precession is not perfectly even. On top of its great circle comes a small nodding of the Earth’s axis, nutation, on an 18.6-year rhythm, the cycle of the Moon’s nodes: it pushes the equinox point forward or back by about 17 seconds of arc at most. The mean ayanamsa ignores it; the true ayanamsa includes it, and matches the real sky on the day of birth.

The site calculates your Vedic chart with the true Lahiri ayanamsa, mean nodes for Rahu and Ketu, and whole-sign houses counted from the Ascendant of each chart. The same ayanamsa is used for all twenty divisional charts, for the Moon’s nakshatra, and therefore for the dashas.

What a few minutes of arc change: nothing in the D1, a lot in the D60

A difference in ayanamsa moves every position by the same amount, but its effect depends on how fine the chart is. In the D1, the Rasi, a sign spans 30°: your Vedic signs almost never move. Divisional charts, on the other hand, divide each sign into finer and finer parts: one minute of arc weighs nine times more in the D9, sixty times more in the D60.

For the Ascendant, 6′ of ayanamsa are worth about 24 seconds on the clock, since the Ascendant moves one degree every four minutes on average. The choice of ayanamsa therefore weighs like a small error in the birth time: invisible in the D1, decisive for the finest charts.

Take the 6′ between Krishnamurti and Lahiri, and see what they change, chart by chart:

• D1, the Rasi: only a planet within 6′ of the end of its sign moves into the next one, about one in three hundred.
• D9, the [Navamsha](vedique:d9-navamsha), and the padas: with parts of 3°20′, about one planet in thirty changes pada, and so changes sign in the D9.
• D60, the [Shashtiamsha](vedique:d60-shashtiamsha): with parts of 30′, about one planet in five changes part; with the Raman gap, every one of them does.
• The [dashas](vedique:dashas-vimshottari): their dates depend on how far the Moon has already travelled through its nakshatra. 6′ shift them by two weeks to almost two months depending on the birth period, the Raman gap by up to more than two years.

A planet right next to a boundary in a fine chart? Read it with care and give more weight to what the other charts confirm: that is the principle of crossing, explained in crossing the charts.