Science Fair Project Encyclopedia
The Hindu calendar used in Vedic times has undergone many changes in the process of regionalization, and today there are several regional Indian calendars. Mostly, these are inherited from a system first enunciated in Jyotish Vedanga (one of the six adjuncts to the Vedas, 12th to 14th century BC), standardized in the Surya Siddhanta (3rd century) and subsequently reformed by astronomers such as Aryabhata (499), Varahamihira (6th century), Bhaskara (12th century), and Fatehullah Shirazi (16th century).
The Indian Calendar Reform Committee 1957 formalized the Indian National Calendar as well as a religious calendar (referred to as the Rashtriya Panchang). The formality was meant for most civil purposes but is mainly used to determine the holidays of government workers. The latter, like many regional calendars, defines a solar calendar based on the authoritative version of the Surya Siddhanta (edited 10th century). Here months are determined based on the sun's position against the fixed stars (constellations) at sunrise; the sun's position being computed by antipodal observations of the full moon. This sidereal computation avoids having to do leap year adjustments, but the number of days in any given month can vary by one or two days and conversion of dates to Gregorian or day of the week computations requires one to consult an ephemeris. The lay person therefore relies on the panchangs or almanacs produced by authoritative astronomical schools. The word panchang is derived from the sanskrit panchangam (pancha=five, anga=limb), which refers to the five limbs of the calendar: 1. the lunar day, 2. the solar day, 3. the asterism on which the sun rises, 4. the angle of the sun and moon and 5. the half lunar day. Over time, different Brahminical bodies producing the panchang's 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.
In the majority of Indian calendars, a separate thread of luni-solar tithis run concurrently with the solar calendar. While birthdates and the like are recorded in solar terms, the tithis determine the timing of religious rituals. Thus every day is marked with a solar month and date as well as a lunar tithi, corresponding to the position of the moon at sunrise. Religious events are then identified e.g. as "the tenth day of the waxing moon in Ashvin", which is the date for Dussehra. The actual date may fall on Kartik 8 (as in 2004). This is similar to the computation of Easter or the Chinese New Year and unlike that of purely lunar computations such as Eid ul-Fitr, which rotate around the solar year. For non-religious purposes however, the Gregorian calendar is the default, though government books also refer to the Indian National Calendar. In many rural areas however, the traditional calendar continues to hold sway.
Names of months (Indian National Calendar)
The most common names for the twelve months are shown below. In Vedic times, these were lunar months, but since the Surya Siddhanta they are computed on a solar basis. The later months are shorter because on the average, the Sun's motion is more rapid when it is at perihelion.
| Month Name |
| Month day 1|
| Number |
| Season |
Note that this table is an agglomeration of disparate entities. The first day and number of days in each month is from the Indian National Calendar which is based on the Vikram calendar. Note that in leap years (which coincide with the Gregorian), the first month of Chaitra has 31 days instead of 30, and starts on March 21 instead of March 22. The association of seasons or ritus with months is based on religious calendars (including the Rashtriya Panchang, which has Vaisakha as the first month) – the six ritus of two months each constitutes the rituchakra (the cycle of the seasons): Grishma (summer), Varsha (rains), Sarat (autumn), Hemanta (late autumn), Sisir (dew/winter), Vasanta (spring). Starting the calendar on Vaisakha avoids the split in the season of Vasanta.
The nakshatra-based names of these months (e.g. Chaitra, from Chitraa), reflect the origin of these names in the lunar calendar that was used in Vedic times, when an intercalary month (Purushottam) was added as the adhika maas (extra month) when the lunar year went about 30 days behind the solar calendar. A number of regions still use the purely lunar calendar, but the intercalary is determined as the month in which the sun is in the same rashi on two consecutive dark moons. Thus one may have the two months "Shravana-nija" and "Shravana-adhika" (nija=original, adhika=extra). Lunar months consist of thirty lunar days, or tithis. A lunar day is based on the moon's position in a nakshatra, and the solar day is measured from sunrise to sunrise. In the paksha system, the lunar days are numbered from the full moon and the new moon.
A.L. Basham writes in his The Wonder that was India:
- The vedic calendar had lunar months split into two pakshas of 15 days, with the day (tithi) being designated by the moon phase at sunrise (sometimes a tithi would be skipped if started after sunrise and ended before the next).
The waxing paksha is called shuklapaksha, light half, and the waning paksha the krishnapaksha, dark half. There are two different systems for making the lunar calendar:
- amanta or mukhya mana system – a month begins with a new moon, mostly followed in the southern states
- purnimanta or gauna mana system – a month begins with a full moon, followed more in the North.
The two calendars most widely used in India today are the Vikram calendar followed in North India while South Indian states such as Karnataka, Andhra Pradesh and Tamil Nadu follow the Shalivahana calendar. A variant of the Vikram Calendar was reformed and standardized as the Indian National calendar in 1957 to have constant days in every month (with leap years). Years are counted from 78, year zero of the Saka era. The Bengal Calendar, Bangabda (introduced 1584) is widely used in Eastern India. A reformed version of this calendar, with constant days in each month and a leap year system (1966) serves as the national calendar for Bangladesh. Nepal also follows the Vikram calendar. The same month names and roughly the same periods apply to a number of Buddhist calendars in Sri Lanka, Tibet and other areas.
The traditional Vedic calendar used to start with the month of agrahayan (agra=first + ayan = travel of the sun, equinox) or Margashirshe. This is the month where the Sun crosses the equator, i.e. the vernal equinox. This month was called margashirshe after a nakshatra around lambda Orionis (see below). Due to the precession of the earth's axis, the vernal equinox is now in Pisces, and corresponds to the month of chaitra. This shift over the years is what has led to various calendar reforms in different regions to assert different months as the start month for the year. Thus, some calendars (e.g. Vikram) start with Chaitra, which is the present-day month of the vernal equinox, as the first month. Others may start with Vaisakha (e.g. Bangabda). The shift in the vernal equinox by nearly four months from agrahaayana to chaitra in sidereal terms seems to indicate that the original naming conventions may date to the fourth or fifth millennium BC, since the period of precession in the earth's axis is about 25,800 years.
The ecliptic, the apparent path of the sun through the sky, is divided into 27 nakshatras, or lunar mansions, reflecting the moon's cycle against the fixed stars, 27 days and 7¾ hours. The set of nakshatras, which were well known at the time of the Rig Veda (2nd–1st millenium BC), are as follows (with some of their defining landmarks in the sky):
- Asvini (β and γ Arietis)
- Bharani (35, 39, and 41 Arietis)
- Kr.ttikA / Karthigai (Pleiades)
- Rohini (Aldebaran)
- Mrigashirsha (λ, φ Orionis)
- Ardra (α Orionis - Betelgeuse)
- Punarvasu (α and β Geminorum - Castor, Pollux)
- Pushya (γ, δ and θ Cancri)
- Aslesha (δ, ε, η, ρ, and sigma Hydrae)
- Magha (α, γ, ε, ζ, η, and μ Leonis - Regulus)
- Purva-Phalguni (δ and θ Leonis)
- Uttara-Phalguni (β and 93 Leonis - Denebola)
- Hasta (α to ε Corvi)
- Chitra (Virgo - Spica)
- Svati (Bootes - Arcturus )
- Vishakha (α, β, γ and ι Librae)
- Anuradha (β, δ and π Scorpionis)
- Jyeshtha (α, σ, and τ Scorpionis - Antares)
- Mula (ε, ζ, η, θ, ι, κ, λ, μ and ν Scorpionis)
- Purvasharha (δ and ε Sagittarii)
- Uttarasharha (ζ and σ Sagittarii)
- Sravana (α, β and γ Aquilae - Altair)
- Dhanishtha / SraviShThA / Avittam (α to δ Delphinis)
- Satabhishaj / Chadayam (γ Aquarii etc.)
- Purva-Bhadrapada / Poorattaadhi (α and β Pegasi - Markab)
- Uttara-Bhadrapada / Uttrattadhi (γ Pegasi and α Andromedae - Alpheratz)
- Revati (ζ Piscum)
An additional 28th intercalary nakshatra, Abhijit (α, ε and ζ Lyrae - Vega - between Uttarasharha and Sravana), is required to compensate for the sidereal month being eight hours more than 27 days. Unlike the 13°20' range of the 27 proper nakshatras, Abhijit spans 4°14' to reflect the extra span of 7¾ hours.
The ecliptic is also divided into twelve rashis, equivalent to the twelve signs of the zodiac. The names of these signs correspond to those in the West, and may indicate a common Sumerian origin. Greek astronomical interchange, as in the Romaka Siddhanta, also led to a degree of homogenization. For some time these were also the names of solar months (saura maasa), and now only the calendar of Kerala called the Kollavarsha uses those names for its months; the first month is Simha (Chingam) and the last is Karka(Karkkatakam).
|Simha|| Varsha |
- Indian Calendar Webexhibits.org
- Pandit Sanjay Rath, Some facts on the Hindu Calendar
- Vedic Calendar Program (freeware),  For any modern year, anywhere in the world, tells when each tithi, each naksatra, and each lunar month occurs, and the dates for various festivals (especially Gaudiya Vaisnava). Also calculates birthdays.
- A.L. Basham, The wonder that was India, Appendix II: "Astronomy", Macmillan, 1954. Rupa and Co, Calcutta, reprint.
- S. Balachandra Rao, Indian Astronomy: An introduction, Universities Press, Hyderabad, 2000.
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