The Hindu Calendar, by Ravi Kiran
History: The Hindu Calendar has its origins in Vedānga (a supplement to Vedas) called Jyotisha (literally, “celestial body study”). After the Vedic period, scholars such as Āryabhatta (5th century CE), Varāhamihira (6th century CE) and Bhāskara (12th century CE) contributed to the development of the Hindu Calendar. The most widely used authoritative text for the Hindu Calendars is the Sūrya Siddhānta, thought to have been written around 10th century CE.
Types of calendars: Calendars are typically based on the movement of two prominent celestial bodies — the sun (solar calendar) and the moon (lunar calendar) or a combination of both (lunisolar calendar). The calendar most of us use in daily life with January, February etc. as months is based on the position of Earth relative to Sun during the former’s movement around the latter and is hence a solar calendar. There are more than thirty well-developed Hindu calendars, all variants of the Sūrya Siddhānta based calendars. However, the two most commonly used calendars are the Vikrama calendar and the Shalivahana or Saka calendar. In the Vikrama calendar, the zero year corresponds to 58 BCE, while in the Shalivahana calendar, it corresponds to 78 CE. Both the calendars are lunisolar i.e the date indicates both the moon phase and the time of the solar year.
Eras and Year numbering: Hindus consider time to progress cyclically over four eras or ages — Krita Yuga, Tretā Yuga, Dvāpara Yuga and Kali Yuga. We are currently in Kali Yuga which is supposed to have begun around 3102 BCE, therefore our Kali Yuga year (as of 2007) would be 5109. Apart from this numbering system, there is also a cycle of 60 calendar year names, called Samvatsaras, which start at the first year of the yuga and run continuously. These go by the names — Prabhava, Vibhava, Shukla etc. 2007 happens to be Sarvajit Nama Samvatsara.
Months of lunisolar calendar: When a new moon occurs before sunrise on a day, that day is said to be the first day of the lunar month. A lunar month has 29 or 30 days (according to the movement of the moon). There are twelve lunar month names — Chaitra,Vaishākha, Jyaishtha, Āshādha, Shrāvana, Bhādrapada, Āshwina, Kārtika, Mārgashīrsha, Pausha, Māgha,Phālguna. Determining which name a lunar month takes is somewhat indirect and based on the rāshis. Rāshis correspond to 12 Zodiac signs in cosmology. The day on which the Sun transits into each rāshi before sunset is taken to be the first day of the month. The rāshis are : Mesha(Aries),Vrushabha (Taurus), Mithuna(Gemini), Karka(Cancer), Simha(Leo), Kanya(Virgo), Tula(Libra), Vruschika(Scorpio), Dhanu(Sagittarius), Makara (Capricornus), Kumbha (Aquarius) and Meena(Pisces). The time and date when Sun enters Mesha in the lunar month of Chaitra is traditionally observed as the New Year. Depending on the particular Hindu calendar, this is usually around 22nd March or 15th April.
Day specification in the Hindu calendar: The Hindu calendrical day starts with local sunrise. It is allotted five “properties”, called angas. They are: the ‘tithi‘ active at sunrise, the ‘vaasara‘ or weekday, the nakshatra in which the moon resides at sunrise, the yoga active at sunrise, the karana active at sunrise. It is from these that we arrive at the word for Hindu calendar - panchang. As we have seen before, the time the moon takes for each revolution around the earth is considered a month. The month is divided into two phases or pakshas depending on the phase of the moon. When the moon is waxing (becoming brighter) the month is in Shukla paksha and when it is waning, it is in Krishna paksha. Each paksha is divided into 15 tithis. The first 14 tithis are Sanskrit numbers for 1 to 14 (Prathama,Dvitiya etc.). The 15th tithi of Shukla paksha is Poornima (full moon) and the 15th tithi of Krishna paksha is Amavasya (new moon). There are 7 vāsaras : Ravi (Sunday), Soma (Monday), Mangala (Tuesday), Budha(Wednesday),Guru (Thursday), Shukra(Friday), Shani(Saturday). The nakshatra is the zodiac constellation in which the moon is found on the particular day at the time of sunrise. There are 27 such constellations and go by names such as Ashvinī, Bharanī, Hasta etc. The yoga is based on the longitudes of sun and moon. There are 27 such yogas. The karana is the time required for the angular distance between the sun and the moon to increase in steps of 6° starting from 0°.
Pay attention to these names the next time you come across a Hindu calendar or during a puja ceremony. During Sankalpam — one of the phases of a puja , the priest chants the details of samvatsar(year), ayana(the arc between different zodiacs), rutu(season), masa(month), paksha(fortnight), tithi(position in fortnight), vasara(day), shubha-nakshatra(moon’s zodiac constellation). By doing so, he/she ties down the occasion to the precise date it is performed.
An important aspect of the Hindu calendar, which perhaps is not immediately apparent from the article, is the amount of precision and detail it offers. This is obviously not possible without an advanced understanding of astronomy. That this calendar has been in vogue for thousands of years with very little changes speaks volumes about the competence of early Hindu astronomers and pioneers of the Hindu calendric system.
References: http://en.wikipedia.org/wiki/Hindu_calendar, 2007 calendar released by HTCC(http://www.htccwa.org)
Ravi Kiran is a PhD student at the Computer Science Department at University of Washington. You can reach him at kiran@cs.washington.edu
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