Bengali calendar

The Bengali calendar or Bangla calendar (Bengali: বঙ্গাব্দ, romanized: Bôṅgābdô, colloquially বাংলা সন, Bāṅlā Sôn or বাংলা সাল, Bāṅlā Sāl, "Bangla Year") is a solar calendar used in the Bengal region of the Indian subcontinent. In contrast to the traditional Indian Hindu calendar, which begins with the month Chaitra, The Bengali calendar starts with Baishakh. A revised version of the Bangladeshi calendar is officially used in Bangladesh, while an earlier, traditional version continues to be followed in the Indian states of West Bengal, Tripura, and Assam. The Bengali calendar began in 590–600 CE to commemorate the ascension of Shashanka, the first independent king in Bengal's unified polity. Some modifications were done to the original calendar during Mughal emperor Akbar's era, to facilitate the collection of land revenue at the start of the Bengali harvesting season. The first day of the Bengali year is known as Pohela Boishakh (1st of Boishakh) which is a public holiday in Bangladesh.

The Bengali era is called Bengali Sambat (BS) and has a zero year that starts in 593/594 CE. It is 594 less than the AD or CE year in the Gregorian calendar if it is before Pohela Boishakh, or 593 less if after Pohela Boishakh.

The Saka Era was widely used in Bengal, prior to the arrival of Muslim rule in the region, according to various epigraphical evidence. The Bikrami calendar was in use by the Bengali people of the region. This calendar was named after king Vikramaditya with a zero date of 57 BCE. In rural Bengali communities, the Bengali calendar is credited to "Bikromaditto", like many other parts of India and Nepal. However, unlike these regions where it starts in 57 BCE, the modern Bangladeshi and Bengali calendar starts from 593 CE suggesting that the starting refers the Bengali king Shashaka's ascent to throne.

Some historians attribute the Bengali calendar to the 7th century Bengali king Shashanka, whose reign covered the Bengali era of 594 CE. The term Bangabda (Bangla year) is found too in two Shiva temples many centuries older than Akbar era, suggesting that a Bengali calendar existed long before Akbar's time.

Hindus developed a calendar system in ancient times. Jyotisha, one of the six ancient Vedangas, was the Vedic era field of tracking and predicting the movements of astronomical bodies in order to keep time. The ancient Indian culture developed a sophisticated time keeping methodology and calendars for Vedic rituals.

The Hindu Vikrami calendar is named after king Vikramaditya and starts in 57 BCE. In rural Bengali communities of India, the Bengali calendar is credited to "Bikromaditto", like many other parts of India and Nepal. However, unlike these regions where it starts in 57 BCE, the Bengali calendar starts from 593 suggesting that the starting reference year was adjusted at some point.

Various dynasties whose territories extended into Bengal, prior to the early 13th-century, used the Vikrami calendar. For example, Buddhist texts and inscriptions created in the Pala Empire era mention "Vikrama" and the months such as Ashvin, a system found in Sanskrit texts elsewhere in ancient and medieval Indian subcontinent.

Hindu scholars attempted to keep time by observing and calculating the cycles of the Sun (Surya), Moon, and the planets. These calculations about the Sun appear in various Sanskrit 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 complete sometime between the 5th century and 10th century.