There are many variations of Hindu calendars (also called Indian calendars). Some regions use a solar calendar based on what are the signs of the Zodiac in English. Other regions use a luni-solar calendar with months based on the lunar cycle and years of either 12 or 13 months. The Gregorian calendar is also widely used in India for civil purposes.

Many Hindus use both a lunar and a solar calendar simultaneously, as part of a panchangam. The word means "five limbs." The five parts of a panchangam depend on: 1. the lunar day, 2. the lunar month, 3. the half-day, 4. the angle of the sun and moon, and 5. the solar day.
Some lunar calendars start each month with a new moon, while others start each month with a full moon, and Hindu calendars don't all agree on when a year starts, either.

In an attempt to get everyone in India to use the same calendar, the government introduced an Indian National calendar in 1957. It is a solar calendar with either 365 or 366 days in a year, leap year rules identical to those in the Gregorian calendar, but with years starting near the vernal equinox (March 22 in regular years, March 21 in leap years) and traditional Indian names for the months. Years are counted from the first year of the Saka era, (AD 78) The year is also divided into 6 seasons of two months each.

The ecliptic, the apparent path of the sun through the sky, is dividied into 12 rashi, which are the same as the signs of the zodiac in English. The solar months are based on the rashi.

The ecliptic is also divided into 27 lunar mansions, the nakshatra, which means stars in English. However, paradoxically, the nakshatras sometimes also refer to zodical constellations (for more information on Astrology please click here ). There are approximately 3 nakshatras in each rashi. Each nakshatra has four divisions knowns as paadams. Some nakshatras spill over two rashis based on which paadam they come under.

1. Ashwini
2. Bharani
3. Krittika/ Karthigai
4. Rohini
5. Mrigashirsha
6. Ardra
7. Punarvasu
8. Pushya
9. Ashlesha
10. Magha
11. Purva Phalguni
12. Uttara Phalguni
13. Hasta
14. Chitra
15. Swati
16. Vishakha
17. Anuradha
18. Jyeshta
19. Moola
20. Purvashadha
21. Uttarashadha
22. Shravana
23. Dhanistha/ Avittam
24. Shatabhishak/ Chadayam
25. Purva Bhadrapada/ Poorattaadhi
26. Uttara Bhadrapada/ Uttrattadhi
27. Revati

The lunar months, are named for twelve of the nakshatra. Purushottam is the adhika maas (extra month) added when the lunar months have gotten about 30 days behind in the solar calendar. Lunar months consist of thirty lunar days, or tithis. (Lunar days are not the same length as solar days) In some calendars, lunar months are simply numbered, not named.

Lunar months are measures from one New Moon to the next (although some groups reckon from the Full Moon). Each lunar month is given the name of the solar month in which the lunar month begins. Because most lunations are shorter than a solar month, there is occasionally a solar month in which two New Moons occur. In this case, both lunar months bear the same name, but the first month is described with the prefix adhika, or intercalary. Such a year has thirteen lunar months. Adhika months occur every two or three years following patterns described by the Metonic cycle or more complex lunar phase cycles.

Each year during Kartik Purnima, which is the full moon in the Indian calendar month of Kartika, thousands of Rajputs lead their camels across the desert to the town of Pushkar for the annual camel fair. They come to sell, buy, and trade animals.

Lunations are divided into 30 tithis, or lunar days. Each tithi is defined by the time required for the longitude of the Moon to increase by 12o over the longitude of the Sun. Thus the length of a tithi may vary from about 20 hours to nearly 27 hours. During the waxing phases, tithis are counted from 1 to 15 with the designation Sukla. Tithis for the waning phases are designated Krsna and are again counted from 1 to 15. Each day is assigned the number of the tithi in effect at sunrise. Occasionally a short tithi will begin after sunrise and be completed before the next sunrise. Similarly a long tithi may span two sunrises. In the former case, a number is omitted from the day count. In the latter, a day number is carried over to a second day.

Rules for Civil Use

In addition to establishing a civil calendar, the Calendar Reform Committee of India set guidelines for religious calendars, which require calculations of the motions of the Sun and Moon. Tabulations of the religious holidays are prepared by the India Meteorological Department and published annually in The Indian Astronomical Ephemeris.

Years are counted from the Saka Era; 1 Saka is considered to begin with the vernal equinox of C.E. 78. The reformed Indian calendar began with Saka Era 1879, Caitra 1, which corresponds to C.E. 1957 March 22. Normal years have 365 days; leap years have 366. In a leap year, an intercalary day is added to the end of Caitra. To determine leap years, first add 78 to the Saka year. If this sum is evenly divisible by 4, the year is a leap year, unless the sum is a multiple of 100. In the latter case, the year is not a leap year unless the sum is also a multiple of 400. The table below gives the sequence of months and their correlation with the months of the Gregorian calendar.

* In a leap year, Caitra has 31 days and Caitra 1 coincides with March 21.

Principles of the Religious Calendar

Religious holidays are determined by a lunisolar calendar that is based on calculations of the actual postions of the Sun and Moon. Most holidays occur on specified lunar dates (tithis), as is explained later; a few occur on specified solar dates. The calendrical methods presented here are those recommended by the Calendar Reform Committee (1957). They serve as the basis for the calendar published in The Indian Astronomical Ephemeris. However, many local calendar makers continue to use traditional astronomical concepts and formulas, some of which date back 1500 years.

The Calendar Reform Committee attempted to reconcile traditional calendrical practices with modern astronomical concepts. According to their proposals, precession is accounted for and calculations of solar and lunar position are based on accurate modern methods. All astronomical calculations are performed with respect to a Central Station at longitude 82°30' East, latitude 23°11' North. For religious purposes solar days are reckoned from sunrise to sunrise.

A solar month is defined as the interval required for the Sun's apparent longitude to increase by 30o, corresponding to the passage of the Sun through a zodiacal sign (rasi). The initial month of the year, Vaisakha, begins when the true longitude of the Sun is 23° 15' (see table below). Because the Earth's orbit is elliptical, the lengths of the months vary from 29.2 to 31.2 days. The short months all occur in the second half of the year around the time of the Earth's perihelion passage.

History of the Indian Calendar

The history of calendars in India is a remarkably complex subject owing to the continuity of Indian civilization and to the diversity of cultural influences. In the mid 1950s, when the Calendar Reform Committee made its survey, there were about 30 calendars in use for setting religious festivals for Hindus, Buddhists, and Jainists. Some of these were also used for civil dating. These calendars were based on common principles, though they had local characteristics determined by long-established customs and the astronomical practices of local calendar makers. In addition, Muslims in India used the Islamic calendar, and the Indian government used the Gregorian calendar for administrative purposes.

Early allusions to a lunisolar calendar with intercalated months are found in the hymns from the Rig Veda, dating from the second millennium BCE. Literature from 1300 BCE to CE 300, provides information of a more specific nature. A five-year lunisolar calendar coordinated solar years with synodic and sidereal lunar months.

Indian astronomy underwent a general reform in the first few centuries CE, as advances in Babylonian and Greek astronomy became known. New astronomical constants and models for the motion of the Moon and Sun were adapted to traditional calendric practices. This was conveyed in astronomical treatises of this period known as Siddhantas, many of which have not survived. The Surya Siddhanta, which originated in the fourth century but was updated over the following centuries, influenced Indian calendrics up to and even after the calendar reform of 1957 CE.

Please NOTE that the above information is just a brief explanation of the Indian calendar. More information can be found at libraries.

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