Chandra

your festivals move because the sun and moon refuse to divide evenly.

scrub decades of lunar drift and watch adhik maas get inserted to fix it

Twelve lunar months add up to 354.37 days, ten days and change short of the 365.24-day solar year, so a calendar that only counts moons drifts through the seasons — which is why Ramzan currently falls further earlier each year. A calendar that only counts the sun never drifts, but then it has no moon in it to schedule anything by. The Indian panchang refuses to give up either: it tracks the moon, and whenever the drift builds past one lunar month, it inserts a whole extra month — adhik maas — to pull itself back in line with the sun.

Concepts: moon, chronology.

An interactive you play with one thumb, on Wundr.