Afs I don't know what calendar you have there, but we have something like that as well. It is a lunar calendar and the birthdays are based on a "star" (I guess they are constellations rather, I don't know but we call them stars). There are 27 "stars" and each year the birthday falls on a completely different date, not just a day here or there. It is all very confusing. My father studied astronomy and he is very patient in explaining me the Indian system of stars, lunar cycles, solar cycles etc a million times. I understand it well when he explains, but cannot remember a thing afterwards It is very interesting, but complex at the same time. The western calendar is all I can handle I guess. BTW, not everyone followed lunar cycles traditionally in India, I think the majority followed a solar calendar, but not the western one.