The festival date is set according to the ..... Bengali calendar as the first day of its first month Boishakh.

The Bengali calendar is a lunisolar calendar, which means it is based on both the phases of the moon and the position of the sun. This type of calendar system is used in many cultures around the world, particularly in South Asia, to determine important dates and festivals. The lunisolar calendar is designed to keep the months in alignment with the seasons, which is why it incorporates both lunar and solar cycles.

In the context of the Bengali calendar, the first day of the year, known as Pohela Boishakh, is celebrated on the first day of the month Boishakh. This date is determined by the lunisolar calendar, which ensures that the festival aligns with both the lunar phases and the solar year. The lunisolar calendar is necessary because a purely lunar calendar would drift relative to the solar year, causing the months to shift out of alignment with the seasons over time. Similarly, a purely solar calendar would not account for the moon's phases, which are important for many cultural and religious observances.

The lunisolar calendar system used in the Bengali context is a sophisticated method of timekeeping that has been in use for centuries. It is not only used to determine the date of Pohela Boishakh but also to set the dates for other important festivals and events throughout the year. Understanding the lunisolar calendar is crucial for anyone studying West Bengal's culture, history, and traditions, as it plays a significant role in the region's social and religious life.

In summary, the Bengali calendar is a lunisolar calendar, which means it is based on both the phases of the moon and the position of the sun. This system ensures that the first day of the Bengali New Year, Pohela Boishakh, is accurately determined and celebrated on the first day of the month Boishakh, aligning with both lunar and solar cycles.