indian calendar

Okay I was partially right, the calendar does use the moon and sun.  Here is more detail, Ashley had sent me a document on Indian Holidays:

The Indian calendar is ingeniously based on both the sun and the moon; it uses a solar year but divides it into 12 lunar months. A lunar month is precisely 29 days 12 hours 44
minutes and 3 seconds long. Twelve such months constitute a lunar year of 354 days 8 hours 48 minutes and 36 seconds. To help the lunar months coincide with the solar year,
the practice of inserting an intercalary (extra) month arose. So 60 solar months = 62 lunar months. Hence an extra month, called the Adhik Mas, is inserted every 30 months
i.e. every 2 ½ years.
Lunar days in the Indian calendar are called tithis. They are calculated using the difference of the longitudinal angle between the position of the sun and moon. Because of this, tithis may vary in length. Consequently, the tithi mayor maynot have changed by the time the day has changed at sunrise. And that is why we find at certain times a tithi being omitted, and at certain times, two consecutive days sharing the same tithi.
In the Indian calendar, seasons follow the sun; months follow the moon; and days, both the sun and the moon. The era in the Indian calendar is called the Vikram Era, or the
Vikram Samvat as it is called, which began in 57 BCE. To calculate the corresponding year of the Common Era, 57 years should be subtracted from the Indian year if the date
falls between the beginning of the Indian year and the end of the Western year i.e.between Kartak sud 1 and 31 December. If the date falls between the beginning of the Western year and the end of the Indian year i.e. between 1 January and Aaso vad 30, then only 56 years should be subtracted.

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