Indian national calendar

The Indian national calendar (sometimes called Saka calendar) is the official civil calendar in use in. It is used, alongside the, by the , news broadcasts by , and calendars and communications issued by the. Beside such formal purposes, the calendar is not very widely used.

The term may also ambiguously refer to the, and the is commonly used by different calendars as well.

Calendar structure
In leap years, Chaitra has 31 days and starts on instead. The months in the first half of the year all have 31 days, to take into account the slower movement of the sun across the at this time.

The names of the months are derived from older, s, so variations in spelling exist, and there is a possible source of confusion as to what calendar a date belongs to.

Years are counted in the, which starts its in the year  of the. To determine leap years, add 78 to the Saka year - if the result is a leap year in the Gregorian calendar, then the Saka year is a leap year as well.

Adoption
The calendar was introduced by the Calendar Reform Committee in, as part of the Indian Ephemeris and Nautical Almanac, which also contained other astronomical data, as well as timings and formulae for preparing , in an attempt to harmonise this practice. Despite this effort, local variations based on older sources such as the may still exist.

Usage officially started at Chaitra 1, 1879 Saka Era, or. However, government officials seem to largely ignore the of this calendar in favour of the religious calendar.

Rashtriya Panchang
The Reform Committee also formalised a religious calendar, referred to as the Rashtriya Panchang. This, like many regional calendars, defines a based on the authoritative version of the  from the 10th century.

The word panchang is derived from the Sanskrit panchangam (pancha, five; anga, limb), which refers to the five limbs of the calendar: the, the , the half-day, the angle of the sun and moon, and the.

In the Rashtriya Panchang, months are determined based on the sun's position against the at sunrise, computed by antipodal observations of the full moon. This sidereal computation avoids fixed leap year rules, but the number of days in any given month can vary by one or two days. Conversion of dates to the, or computing the day of the week, requires one to consult the. The lay person therefore relies on the panchangs or s produced by authoritative astronomical schools.

Over time, different ical bodies producing the panchangs have varied in their geographical center and other aspects of the computation, resulting in a divergence of a few days in the different regional calendars. Even within the same region, there may be more than one competing authority, occasionally resulting in disagreement on festival dates by as much as a month. The Rashtriya Panchang seeks to resolve such differences.

Reference

 * Mapping Time: The Calendar and its History by E.G. Richards (ISBN 0-19-282065-7), 1998, pp. 184-185.