How to calculate a birth nakshatra and pada from Moon longitude

Begin with the Moon's sidereal longitude at the birth instant. Obtaining that longitude needs a reliable instant conversion, an ephemeris and a chosen ayanamsa. This page begins after that calculation; the notebook classifies a coordinate you supply and does not calculate a birth chart from a date.

One circle is 21,600 arcminutes. Dividing it into 27 equal sectors gives 800 arcminutes per nakshatra. Dividing a sector into four gives 200 arcminutes per pada.

An invented Moon at 19° Aries has longitude 1,140 arcminutes.

1. Sector index: floor(1140 ÷ 800) = 1. Counting Ashwini as index 0 makes index 1 Bharani.
2. Offset within the sector: 1140 − 800 = 340 arcminutes.
3. Pada: floor(340 ÷ 200) + 1 = 2.

The Moon is therefore Bharani, pada 2 in this example. The notebook below uses whole degrees and arcminutes so you can reproduce those divisions without silently rounding a decimal.

Use half-open intervals: include the starting point and exclude the ending point. At exactly 13°20′ Aries, Ashwini has ended and Bharani begins. At exactly 3°20′ within a nakshatra, pada 2 begins. At a completed 360°, normalize back to 0° before classification.

Keep higher precision when using a real ephemeris. The notebook's one-arcminute grid is educational and cannot resolve positions separated by arcseconds. Do not use an approximate value to settle a close boundary dispute.

Find every sector in the 27-star table. If providers disagree, compare Lahiri and Raman and the numeric longitudes before comparing interpretations.