Thai Lunar (Suriyayart)

Sets Vesak and the uposatha days · arithmetic, not observed

The calendar that actually fixes the Buddhist observances — Vesak, Asalha Bucha, Magha Bucha, and the uposatha days that fall on each new and full moon. Twelve numbered months alternate 29 and 30 days, each running fifteen waxing days to the full moon and then waning back to the dark; an intercalary day is added to month 7 in some years, and in others a whole second month 8 (shown here as 8²), which is where Asalha Bucha moves when it appears. It is calculated, not observed: the months open where the Suriyayart arithmetic says they open, which is why an astronomical reckoning of the same calendar can land a day off the date temples actually keep. Note the pair it makes with the Thai Buddhist calendar above — same era, same country, one solar and civil, this one lunar and liturgical.

Does something here look wrong? Tell us about the Thai Lunar (Suriyayart) calendar.