How nakshatra is calculated

Divide the Moon's sidereal longitude into 27 arcs of 13 degrees 20 minutes. The arc it falls in is the nakshatra.

Each nakshatra is further cut into four padas of 3 degrees 20 minutes, which is what a birth chart is naming when it gives a pada.

Unlike tithi, this one is sensitive to the ayanamsha — the offset between the tropical and sidereal zodiacs. The Moon's longitude has to be converted before the division happens, and a different offset moves every boundary.

Lahiri is not one number

Most Indian almanacs and apps say they use Lahiri, which sounds like agreement. It is not quite.

On 13 September 2026, Drik prints 24.236787°. The Swiss Ephemeris variant we use agrees with that to about 1.3 arcseconds. But the library's own SIDM_LAHIRI constant gives 24.230049° — a difference of roughly 24 arcseconds.

Twenty-four arcseconds sounds like nothing. At a sankranti it is about ten minutes of the Sun's motion, which is enough to move a festival across a sunrise. This is the kind of discrepancy that produces two confident almanacs and one confused reader.

The other ayanamshas

Raman runs about 1.5 degrees less than Lahiri. The Surya Siddhanta carries its own ayana. Vakya almanacs do not state one explicitly at all, because the question does not arise the same way in a mean-motion system.

What we do

We compute drik under Lahiri, using the variant that matches what the major almanacs print, and the exact figure belongs beside the value, because the word "Lahiri" alone is not a number.