Most calendars use fixed, pre-printed dates. santalicalendar.com is different — it watches the actual Sun and Moon positions in the sky right now, and calculates dates fresh every time. This means moon phases, Santali month names, and even the 13th leap month (Badiya Bonga) are always accurate — automatically, for any year.
Earth spins like a top — and like any top, it slowly wobbles. Over centuries, this wobble shifts the star map by about 24 degrees.
Western calendars ignore this shift. But traditional Santali astronomy tracks the actual stars you see in the sky. So our calendar subtracts this drift every single day:
This correction is called Lahiri Ayanamsa. Without it, festival dates would slowly drift away from the real sky over time.
The Moon doesn't move at a steady speed — it speeds up and slows down depending on how close it is to Earth. So we can't just add 29.5 days to find the next New Moon.
Instead, we calculate the exact angle between the Sun and Moon in real-time:
We use precise astronomical equations (Jean Meeus method) to find these exact moments — accurate to the nearest second, not just the nearest day.
A lunar month is ~29.5 days. A solar year is 365 days. So 12 lunar months = only 354 days — 11 days short every year.
To keep festivals in the right season, every ~2.7 years we add a 13th extra month. But which month gets doubled? We use a simple rule:
Our app works on phones worldwide. Different countries have different timezones, so "midnight" is a different moment everywhere.
The bug: In India (IST, +5:30 hrs), midnight on our phone = 6:30 PM the previous day in global time (UTC). If a New Moon occurs at 7:00 PM UTC, our app would think it's still in the old month — wrong!
The fix: We always calculate from 12:00 noon (midday) instead of midnight. Noon is safely in the middle of the day — never confused by timezone shifts.
This small change ensures the correct month shows up on every phone in every country.
Think of the Sun and Moon as two runners on a circular track. The Moon is faster — one lap every 29.5 days. The Sun takes 30.4 days. Every time the Moon catches up and passes the Sun, that is a New Moon — and the start of a new Santali month.
Imagine a clock that loses 1 minute every year. After 100 years it shows the wrong time by 1 hour 40 minutes. Earth's spin has this same slow drift. Our calendar applies a small daily correction (Lahiri Ayanamsa) to keep star positions matching what you actually see in the night sky.