Hindu calendar
The Hindu calendar, also called Panchanga, is one of various lunisolar calendars that are traditionally used in the Indian subcontinent and Southeast Asia, with further regional variations for social and Hindu religious purposes. They adopt a similar underlying concept for timekeeping based on sidereal year for solar cycle and adjustment of lunar cycles in every three years, but differ in their relative emphasis to moon cycle or the sun cycle and the names of months and when they consider the New Year to start. Of the various regional calendars, the most studied and known Hindu calendars are the Shalivahana Shaka found in the Deccan region of Southern India and the Vikram Samvat found in Nepal and the North and Central regions of India – both of which emphasize the lunar cycle. Their new year starts in spring. In regions such as Tamil Nadu and Kerala, the solar cycle is emphasized and this is called the Tamil calendar and Malayalam calendar and these have origins in the second half of the 1st millennium CE. A Hindu calendar is sometimes referred to as Panchangam, which is also known as Panjika in Eastern India.
The ancient Hindu calendar conceptual design is also found in the Babylonian calendar, the Chinese calendar, and the Hebrew calendar, but different from the Gregorian calendar. Unlike the Gregorian calendar which adds additional days to the month to adjust for the mismatch between twelve lunar cycles and approximately 365 solar days, the Hindu calendar maintains the integrity of the lunar month, but inserts an extra full month, once every 32–33 months, to ensure that the festivals and crop-related rituals fall in the appropriate season.
The Hindu calendars have been in use in the Indian subcontinent since Vedic times, and remain in use by the Hindus all over the world, particularly to set Hindu festival dates. Early Buddhist communities of India adopted the ancient Vedic calendar, later Vikrami calendar and then local Buddhist calendars. Buddhist festivals continue to be scheduled according to a lunar system. The Buddhist calendar and the traditional lunisolar calendars of Cambodia, Laos, Myanmar, Sri Lanka and Thailand are also based on an older version of the Hindu calendar. Similarly, the ancient Jain traditions in their calendar have followed the same lunisolar system as the Hindu calendar for festivals, texts and inscriptions. However, the Buddhist and Jain timekeeping systems have attempted to use the Buddha and the Mahavira's lifetimes as their reference points.
The Hindu calendar is also important to the practice of Hindu astrology and zodiac system. It is also employed for observing the auspicious days of deities and occasions of fasting, such as Ekadashi.
Origins
The Vedic culture developed a sophisticated time keeping methodology and calendars for Vedic rituals, and timekeeping as well as the nature of solar and Moon movements are mentioned in Vedic texts. For example, Kaushitaki Brahmana chapter 19.3 mentions the shift in the relative location of the Sun towards north for 6 months, and south for 6 months.Time keeping was important to Vedic rituals, and Jyotisha was the Vedic era field of tracking and predicting the movements of astronomical bodies in order to keep time, in order to fix the day and time of these rituals. This study is one of the six ancient Vedangas, or ancillary science connected with the Vedas.
Yukio Ohashi states that this Vedanga field developed from actual astronomical studies in the ancient Vedic Period. The texts of Vedic Jyotisha sciences were translated into the Chinese language in the 2nd and 3rd centuries CE, and the Rigvedic passages on astronomy are found in the works of Zhu Jiangyan and Zhi Qian. According to Subhash Kak, the beginning of the Hindu calendar was much earlier. He cites Greek historians describing Maurya kings referring to a calendar which originated in 6676 BCE known as Saptarsi calendar.
The Vikrami calendar is named after king Vikramaditya and starts in 57 BCE.
Texts
Hindu scholars kept precise time by observing and calculating the cycles of Surya, Moon and the planets. These calculations about the Sun appear in various astronomical texts in Sanskrit, such as the 5th-century Aryabhatiya by Aryabhata, the 6th-century Romaka by Latadeva and Panca Siddhantika by Varahamihira, the 7th-century Khandakhadyaka by Brahmagupta and the 8th-century Sisyadhivrddida by Lalla. These texts present Surya and various planets and estimate the characteristics of the respective planetary motion. Other texts such as Surya Siddhanta dated to have been completed sometime between the 5th century and 10th century present their chapters on various deified planets with stories behind them.The manuscripts of these texts exist in slightly different versions. They present Surya, planet-based calculations and Surya's relative motion to Earth. These vary in their data, suggesting that the texts were open and revised over their lives. For example, the 1st millennium CE Hindu scholars calculated the sidereal length of a year as follows, from their astronomical studies, with slightly different results:
| Hindu text | Estimated length of the sidereal year |
| Surya Siddhanta | 365 days, 6 hours, 12 minutes, 36.56 seconds |
| Paulica Siddhanta | 365 days, 6 hours, 12 minutes, 36 seconds |
| Paracara Siddhanta | 365 days, 6 hours, 12 minutes, 31.50 seconds |
| Arya Siddhanta | 365 days, 6 hours, 12 minutes, 30.84 seconds |
| Laghu Arya Siddhanta | 365 days, 6 hours, 12 minutes, 30 seconds |
| Siddhanta Shiromani | 365 days, 6 hours, 12 minutes, 9 seconds |
The Hindu texts used the lunar cycle for setting months and days, but the solar cycle to set the complete year. This system is similar to the Jewish and Babylonian ancient calendars, creating the same challenge of accounting for the mismatch between the nearly 354 lunar days in twelve months, versus over 365 solar days in a year. They tracked the solar year by observing the entrance and departure of Surya in the constellation formed by stars in the sky, which they divided into 12 intervals of 30 degrees each. Like other ancient human cultures, Hindus innovated a number of systems of which intercalary months became most used, that is adding another month every 32.5 months on average. As their calendar keeping and astronomical observations became more sophisticated, the Hindu calendar became more sophisticated with complex rules and greater accuracy.
According to Scott Montgomery, the Siddhanta tradition at the foundation of Hindu calendars predate the Christian era, once had 18 texts of which only 5 have survived into the modern era. These texts provide specific information and formulae on motions of Sun, Moon and planets, to predict their future relative positions, equinoxes, rise and set, with corrections for prograde, retrograde motions, as well as parallax. These ancient scholars attempted to calculate their time to the accuracy of a truti. In their pursuit of accurate tracking of relative movements of celestial bodies for their calendar, they had computed the mean diameter of the Earth, which was very close to the actual 12,742 km.
Hindu calendars were refined during the Gupta era astronomy by Āryabhaṭa and Varāhamihira in the 5th to 6th century. These, in turn, were based in the astronomical tradition of Vedāṅga Jyotiṣa, which in the preceding centuries had been standardised in a number of works known as Sūrya Siddhānta. Regional diversification took place in the medieval period. The astronomical foundations were further developed in the medieval period, notably by Bhāskara II.
Balinese Hindu calendar
Hinduism and Buddhism were the prominent religions of southeast Asia in the 1st millennium CE, prior to the Islamic conquest that started in the 14th century. The Hindus prevailed in Bali, Indonesia, and they have two types of Hindu calendar. One is a 210-day based Pawukon calendar which likely is a pre-Hindu system, and another is similar to lunisolar calendar system found in South India and it is called the Balinese saka calendar which uses Hindu methodology. The names of months and festivals of Balinese Hindus, for the most part, are different, though the significance and legends have some overlap.Astronomical basis
The Hindu calendar is based on a geocentric model of the Solar System. A large part of this calendar is defined based on the movement of the Sun and the Moon around the Earth. Furthermore, it includes synodic, sidereal, and tropical elements. Many variants of the Hindu calendar have been created by including and excluding these elements and are in use in different parts of India.| synodic elements | sidereal elements | tropical elements | |
| saura māna | rāśi, sauramāsa, varṣa | uttarāyaṇa, dakṣiṇāyana, devayāna, pitṛyāṇa, ṛtu | |
| cāndra māna | tithi, pakṣa, candramāsa, varṣa | ||
| nākṣatra māna | dina, ghaṭikā, vighaṭikā, prāṇa | ||
| sāvana māna | dina |
Year: Samvat
Samvat refers to era of the several Hindu calendar systems in Nepal and India, in a similar manner to the Christian era. There are several samvat found in historic Buddhist, Hindu and Jain texts and epigraphy, of which three are most significant: Vikrama era, Old Shaka era and Shaka era of 78 CE.- Vikram Samvat : A northern Indian almanac which started in 57 BCE, and is also called the Vikrama Era. It is related to the Bikrami calendar, and is apocryphally linked to Vikramaditya. The year starts from the month of Baishakh / Vaishakha. This system is common in epigraphic evidence from northern, western, central and eastern Indian subcontinent, particularly after the early centuries of the 1st millennium CE.
- Shaka Samvat: There are two Shaka era systems in scholarly use, one is called Old Shaka Era, whose epoch is uncertain, probably sometime in the 1st millennium BCE because ancient Buddhist, Jain and Hindu inscriptions and texts use it. However, the starting point of Old Shaka Era is a subject of dispute among scholars. The second system is called Saka Era of 78 AD, or simply Saka Era, a system that is common in epigraphic evidence from southern India.
- Saka era of Southeast Asia: The Hindu calendar system in Indonesia is attributed to the legend of Hindus arriving with a sage Aji Saka in 1st-century Java, in March 78 CE. Numerous ancient and medieval era texts and inscriptions found in Indonesian islands use this reference year. In mainland southeast Asia, the earliest verifiable use of Hindu Saka methodology in inscriptions is marked Saka 533 in Ankor Borei, which corresponds to 611 CE, while the Kedukan Bukit inscription in Sumatra, containing three dates in Saka 604, is the earliest known use of the Shaka era in the Indonesian islands. However, these inscriptions only set the floruit for the use of the Shaka era in these places, and the Hindu calendar likely existed in southeast Asia before these dates to be used in important monuments. Further, the Hindu calendar system remained popular among the Hindus through to the 15th century, and thereafter in Bali.
- Indian national calendar : combines many Hindu calendars into one official standardized one, but old ones remain in use.