In 1957, after struggling to deal with dozens or even hundreds of localized calendars and calendar systems in use in India, the Indian government approved an official standard created by its Calendar Reform Committee. This new system, called the Indian Civil Calendar, is a lunisolar calendar modeled after the common Gregorian Calendar.

Epoch

This calendar's epoch is the beginning of the Saka Era, which is used in many traditional Indian calendars. Being the epoch, this date equates to Caitra 1st of the year 1 (see list of months below). The Gregorian equivalent to this era is the equinox of March 22, 79 AD. The adoption date of the Indian Civil Calendar in its own system was on Caitra 1st, 1879 (March 22, 1957).

Years

A normal year in the Indian Civil Calendar is based on the Earth's rotation around the sun, and is therefore 365 days. A leap year is 366 days with the day being added to the end of the month of Caitra. To determine if a year is a leap year, first add 78 to the Saka year. Using this total, you can then determine if it is a leap year using the same system used in the Gregorian Calendar (see leap year).

Months

The months in this calendar system are named after the traditional months in use for centuries, however, in the civil calendar they have been aligned with accurate, though averaged, astronomical measurements. A solar month is defined as the interval required for the sun's apparent longitude to increase by 30°. Since the sun travels on an elliptical orbit, it moves at differing speeds throughout the year. It is for this reason that in the Indian Calendar, five (six in a leap year) of the months in the beginning of the year have 31 days (when the sun is moving it's slowest), and the rest have 30.

Month Name   Days In Month   Gregorian Equivalent       
Caitra       30*             Caitra 1     = March 22* 
Vaisakha     31              Vaisakha 1   = April 21 
Jyaistha     31              Jyaistha 1   = May 22 
Asadha       31              Asadha 1     = June 22 
Sravana      31              Sravana 1    = July 23 
Bhadra       31              Bhadra 1     = August 23 
Asvina       30              Asvina 1     = September 23 
Kartika      30              Kartika 1    = October 23 
Agrahayana   30              Agrahayana 1 = November 22 
Pausa        30              Pausa 1      = December 22 
Magha        30              Magha 1      = January 21 
Phalguna     30              Phalguna 1   = February 20 
* In a leap year, Caitra has 31 days and Caitra 1 coincides with March 21.

Weeks/Days

The Indian Civil Calendar uses a seven day per week system like most of the world.

Day of Week   Equivalent
Raviãra       Sunday
Somavãra      Monday
Mañgalvã      Tuesday
Budhavãra     Wednesday
Guruvã        Thursday
Sukravãra     Friday
Sanivãra      Saturday

Holidays and Lunar Cycles

While this calendar uses the sun for its accuracy, most of India's holidays are based on lunar cycles and/or positions of both the sun and the moon. For this reason, the Indian Calendar Reform Committee also delegated the India Meteorological Department to annually publish proper dates of holidays in The Indian Astronomical Ephemeris. While an excellent resource, many local calendar makers still use formulas that have been passed down for more than a millennium.

Lunar months are based on the new moon, and are named for the solar month in which the new moon occurred. While a rarity, when two new moons occur in the same solar month, both lunar months are given the same name, though the first occurrence is prefixed with "adhika" (intercalary). Even more rare is when no new moon occurs in a solar month. In this case, there is no month named for the equivalent solar month. However, every few decades when this occurs, there is guaranteed to be two new moons either on the preceding or following month, so one of the adhika months simply takes its place.


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References

  • http://www.math.nus.edu.sg/aslaksen/calendar/indian.shtml
  • http://www.fourmilab.ch/documents/calendar/
  • http://webexhibits.org/calendars/calendar-indian.html

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