There are several calendars in use in India, the earliest dating back to the Hindu calendar used in ancient Vedic times. However, the Indian government has officially adopted the Indian National Calendar for civilian use in the country and the Gregorian calendar for administrative purposes. e Indian National Calendar is a modified version of the traditional calendars of India.
The Hindu calendar system was introduced in the Jyotish Vedanga, the section of the Vedas that deals with astronomy and astrology. It was standardised in the Surya Siddhanta, an astronomical treatise written between the 3rd and 4th centuries, and subsequently reformed by astronomers such as Aryabhata in the 5th century and Bhaskara in the 12th century. According to the ancient calendar system, the calendrical day starts with local sunrise.
It has five properties: tithi, vaasara, nakshatra, yoga and karana. Tithi is the lunar day, calculated from the angular difference between the sun and the moon; vaasara or vaara refers to the seven days of the week; the ecliptic or path of the sun through the sky is divided into 27 nakshatra or lunar mansions, similar to zodiac constellations; yoga is calculated from adding the longitude of the sun and the moon and dividing the sum by 27; and karana is half of the tithi. In ancient India, the length of the year ranged from 365.258681 days to 365.258756 days, compared with the modern length of 365.25636 days; the old values are still in use in many traditional Indian calendars.
The traditional calendar plays a key role in the religious activities. It is referred to constantly by priests and religious leaders to calculate the dates of festivals as well as auspicious days and times for important events such as marriages, launching a new venture, filing nominations for elections and performing religious rituals. Both solar and lunar movements are used in the calculation of dates. To bring about uniformity in the use of calendars in India, a reform exercise was undertaken in the 1950s. Many different calendars based on the movements of the sun and moon were in use then, and different assumptions about the length of months and years brought about variations among them. The Indian National Calendar takes of from the Saka Era.
The first year is counted from the first year of the Saka Era in 78. This calendar, with a normal year of 365 days, was adopted by the Indian government on 22 March 1957 along with the Gregorian calendar. The first day of the Indian National Calendar coincides with 22 March in the Gregorian calendar, except in a leap year when it starts on 21 March. The months have a fixed number of days, either 30 or 31. The five months from the second to the sixth have mean lengths over 30.5 days and their lengths are rounded up to 31 days. The remaining months have 30 days.
