A birthday per calendar :)

So, apparently today is my "star" birthday (according to the hindu calendar). So, this got us thinking about how solar and lunar calendars correlate. I've heard my dad talk about this (he's a serious astrology buff), but obviously it didn't stick :)

But why fear when Wikipedia is here! Which taught me the concept of a lunisolar calendar. And that intercalations are not just about adding a day for a leap year, but could also involve adding a week or even a month (like lunisolar calendars do every 2-3 years to match with the solar calendar). Which explains why solar and lunar birthdays are usually within a couple of weeks of each other.

Another interesting fact: apparently some lunisolar calendars can use the state of vegetation (depending on season, I guess) to determine when the leap month needs to be added! The Hindu calendar uses the phase of the moon to determine this.

This illustration of the hindu calendar simplifies a lot of the calculations of festival dates - which fall back by 11 days every year (because the lunar calendar has fixed months, but approximate years compared to the solar calendar).