There are many variations of the Hindu calendar in use in India, depending on region, caste or tradition.The Hindu calendar adopted by the Indian Government is the most commonly used and is consulted to decide the dates of fairs and festivals. This calendar follows the luni-solar system of reckoning, which means that it takes into account the movement of both the sun and moon while calculating the calendar. The dates of the festivals however, are decided on the basis of the movement of the moon. The lunar year consists of 12 months of 29 or 30 days each. Each month begins with the new moon. To keep pace with the solar year however, every 3 years, an extra month is added to the year, making it a 13-month year.
The extra 13th month is called Adhikamasa. A new moon day is called amavasya and the full moon day iscalled purnmashi or purnima. The full moon day is considered extremely auspicious and is spent fasting and praying.
The solar year too consists of 12 months. A solar month is the time taken by the sun to travel from one sign of the zodiac to the next. The day the sun moves into the next zodiac sign is called sankranti. A sankranti is considered extremely auspicious and many special prayers are performed. Makara Sankranti is one of the most important festivals in India.
A solar year is divided into six seasons of two months each: Vasanta (spring) consists of March and April, Grishma (summer) consists of May and June, Varsha (the rains) of July and August, Sharad (autumn) of September and October, Hemanta (winter) of November and December, and Shishira (the cool season) of January and February.
According to Hindu mythology, at the time the world was created, a yagya was performed and everything that existed was put into it. From this yagya arose the three seasons - Vasanta, Grishma, and Hemanta. Vasanta or spring was the first season to have come out of the fire. Today, most Hindus celebrate their new year in Chaitra (March-April) in Vasanta because it is the season in which the world began.
The four rainy months of Ashadha, Shravana, Bhadrapad, and Ashvina are called chaturmasya. This is considered to be the period when the gods go to sleep, and therefore a time to be extremely cautious and careful.
There are seven days in a week: Somvar (Monday), Mangalvar(Tuesday), Budhavar (Wednesday), Brihaspativar (Thursday), Shukravar (Friday), Shanivar (Saturday), Ravivar (Sunday). Each day is based on the name of a deity or sign of the zodiac or planet which presides over that day.
There are many different eras followed by the Hindus. The government calendar follows the Saka era which is believed to have begun with King Salivahana`s accession to the throne. According to the Saka era, the year 1900 AD would be 1823.