The Equinox Walked, and Mesha Stayed

Two calendars sit on the same shelf in March. One of them calls the day the Sun crosses the equator the start of Aries. The other waits. On a Jyotish chart the Sun is still in Meena, and Mesha is weeks away. In January the same household has already lived the other half of this gap. Makar Sankranti, the Sun's entry into sidereal Makara, falls near the middle of the month. The December solstice has already passed.

The gap has a name: ayanamsa. It is the distance, along the ecliptic, between the March equinox and the start of sidereal Mesha.

Two pins in the same sky

The tropical zodiac, the one Western astrology inherited from Hellenistic practice, pins 0 Aries to the March equinox. Seasons stay put. The stars slide behind them. The sidereal zodiac pins the signs to the stars. Mesha stays with its stars. Precession is the reason the two pins come apart.

The Greek astronomer Hipparchus, in the second century BCE, is the person Ptolemy credits with measuring that slide. This part of the account is Hellenistic, and it lives in a Western book, the Almagest. Ptolemy reports that Hipparchus compared star longitudes, Spica among them, with earlier observers, Timocharis and Aristillus, and found the equinoxes moving. Hipparchus put the rate at no less than one degree in a century. The modern rate is about 50 seconds of arc a year, close to one degree in 72 years.

Indian books met the same sky from their own side. The Vedanga Jyotisha puts the winter solstice at Dhanishtha. Later Indian calendars put it at Shravana, the nakshatra to the west. That is the solstice walking through the stars. Classical siddhantas often describe the ayana shift as a swing that reverses, a back-and-forth, rather than a march that only goes one way. A panchang that follows Lahiri uses the march.

The degree a panchang can name

In November 1952 the Council of Scientific and Industrial Research appointed a Calendar Reform Committee under Meghnad Saha, with N. C. Lahiri as secretary. India then had about thirty ways of fixing the same festival. The committee's report, submitted in 1955, works with an ayanamsa of 23 degrees 15 minutes at 21 March 1956. The national Saka calendar that came out of the report was taken up from that day, 1 Chaitra 1878 Saka.

The value printed as Lahiri in Jyotish ephemerides belongs to that reform and to Lahiri's own tables. Its star anchor is Chitra, which is Spica. Other values remain in use. Raman and Krishnamurti differ inside India. Fagan-Bradley, a Western sidereal choice, puts the year of zero separation near 221 CE, where Lahiri's convention puts it near 285 CE. Near a sign boundary, a degree of disagreement moves a planet from one rashi to the next. When this site names a rashi, the value is Lahiri. In 2026 that gap is a little over 24 degrees. A Sun that Western astrology places in the first 24 degrees of Aries is still in sidereal Meena here.

The test is the chart. A Kundli on these pages is sidereal and Lahiri. It will disagree with a tropical Sun-sign column in a Western magazine, because the two columns are pinned to different zeros.

Questions people keep asking

Why is Makar Sankranti in January?

It marks the Sun's entry into sidereal Makara. The tropical solstice, the shortest day, falls in December. Ayanamsa is the distance between those two markers.

Is there a single official ayanamsa?

The Calendar Reform Committee published a working value for 21 March 1956, and government almanacs followed the Lahiri line that grew from that reform. Other schools still print other values. A planet near a boundary should be read in the ayanamsa the astrologer names.