section_path: Calendar structure
section_name: Calendar structure
paragraph_text: Calendar structure
  
  The calendar months follow the signs of the tropical zodiac rather than the sidereal zodiac normally used with the Hindu and Buddhist calendars.
  
  Chaitra is the first month of the calendar and begins on or near the March equinox. Chaitra has 30 days and starts on 22 March, except in leap years, when it has 31 days and starts on 21 March. All months other than Chaitra start on fixed dates in the Gregorian calendar. The months in the first half of the year all average out to having 31 days, to take into account the slower movement of the sun across the ecliptic at this time. This is similar to the Iranian Solar Hijri calendar.
  
  The names of the months are derived from the older Hindu lunisolar calendar, so variations in spellings exist, and there is a possible source of confusion as to what calendar a date belongs to.
  
  The names of the weekdays are derived from the seven classical planets (see Navagraha). The first day of the week is Ravivāra (Sunday). The official calendar reckoned by the government of India has Sunday as the first and Saturday as the last day of the week.
  
  Years are counted in the Shaka era, which starts its year 0 in the year 78 CE of the Common Era. To determine leap years, add 78 to the Shaka year – if the result is a leap year in the Gregorian calendar, then the Shaka year is a leap year as well.