Hindu calendars are calendars common in modern India, they include: Vikram Samvat, Saka era, Kali Yuga era, Nirvana era and others.
In the territory of modern India, many tribes and nationalities were formed in ancient times, which were separated for a long time. The long isolation of the Indian principalities from each other led to the fact that almost every one of them had its own local calendar system. Until recently, the country used several official civil calendars and about thirty local calendars that served to determine the time of various religious holidays and ceremonies. Among them you can find solar, lunar and lunar-solar.
General basics of calculus
The connection with the movement of the Sun is that the duration of a year in the calendar is equal to the time after which the Sun returns to the same star from which the observation began. This period of time is called a sidereal year. It is longer than the tropical year by 20.4 minutes and, according to modern data, is 365.25636 days.
Ancient Indian astronomers did not know the exact duration of the sidereal year and took it as equal to 365.25876 days. This value is indicated in the ancient Indian astronomical treatise "Surya Siddhanta", the author of which is the outstanding astronomer and mathematician Aryabhata. It was used for almost fifteen centuries in many Indian calendars. As a result, the Indian calendar year, which 1,500 years ago began on the spring or autumn equinox (March 21 or September 23), now begins 22-23 days later, around April 12-13 or October 15-16.
In the Hindu calendar, the day begins with sunrise. There are five "qualities" or "extremities" called Angas. They include:
A tithi (one of the 30 divisions of a synodic month) is active at dawn
Vasara (ancient), Vara (modern), as in Ravi-vara, Soma-Vara, etc., or day of the week
Nakshatra (one of the 27 divisions of the ecliptic) in which the moon is at dawn
Yoga (one of 27 subdivisions based on the ecliptic of longitude from the sun and the moon) is active at sunrise
The karana (divisions based on tithi) are active at dawn. Together, the 5 limbs or properties are designated as panchanga (Sanskrit: pañca five). Explanation of terms �