Why we use the Lahiri ayanamsa
The choice of ayanamsa shifts the whole kundli. Our reasoning, with numbers.
Sidereal astrology measures from the fixed stars; tropical measures from the equinox. The gap between them is the ayanamsa, and it grows by about 50 arc-seconds a year. Right now it is a little under 24 degrees — most of a whole rashi.
Which means the choice of ayanamsa is not a detail. Pick a different one and graha near the edge of a rashi move into the next one, and the reading changes with them.
Why Lahiri
- It is the Indian government standard, set by the Calendar Reform Committee in 1955.
- Almost every panchang printed in India uses it, so our numbers can be checked against a physical book.
- It is the default in the software most Indian astrologers already use, which makes disagreement diagnosable.
The alternatives, briefly
Raman sits about 1.1° away from Lahiri; Krishnamurti about 0.1°; Fagan-Bradley about 0.9° in the other direction. None of them is obviously wrong. They simply anchor to a different starting point, and each has a tradition around it.
We did not pick Lahiri because it is truer. We picked it because it is checkable.
What we display
Every chart footer prints the ayanamsa value we used for that date, to the arc-second. If you compare against another package and the degrees differ, the first thing to check is whether both are on Lahiri and both on true node.