• The Indian calendar is known by the Hindu word "panchanga".
  • The calendar is based on the lunar cycle. A day is measured as the period between one sunrise and the next. A month is the period from one moon cycle to the next. A year is measured from the beginning of a season until its return.
  • A lunar month lasts 28 days.
  • A lunar year lasts 12 lunar months or 354 solar days.
Since a period of twelve lunar months fall short of a solar year by 11 days, an additional month is added to the calendar at five-yearly intervals. This month is known as the "adhika".

Each month is divided into the two cycles (waxing and waning) of the moon (new moon to full moon and back). The period of the new moon is called "amavesya" and the period of the full moon is called "purnimavesya".

A season is called a "rtu" (pronounced 'ritu') and there are four seasons in a year. In the course of history two calendar eras have been adopted, they are the vikrama era and the shaka era.

The Shakas were a nomadic tribe of Central Asia who were displaced by the Yue Chi tribe (one of several nomadic tribes who conducted raiding parties into China, resulting in the construction of the Great Wall of China to exclude such intrusions). The displaced Shakas migrated to northern India in the first century BC. The Shakas established rule over large parts of the area. In 58 BC, they were defeated by a local regional king, vikramaditya, who ruled over central India. To commemorate his victory over the Shakas, the king introduced a new calendar era, the vikram era.

Many years later another Shaka king defeated the Vikramaditya dynasty and established a new era, known as the shaka era, the one which is still the official calendar system in India today.

 

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