The traditional New Year in many South and Southeast Asian cultures is based on the sun’s entry into the constellation of Aries, in modern times reckoned to be around 14 April.
As most countries and cultures of South and Southeast Asia are largely influenced by India, the development of their traditional calendars has been strongly influenced by some form of the Hindu calendar. In other Asian calendars, including the Chinese, New Year is based on the vernal equinox in the northern hemisphere. The Hindu calendar, however, is based on the sidereal year or the movement of the sun relative to the stars.
The Sidereal New Year is celebrated in several states of India, Nepal, Bangladesh, Sri Lanka, Pakistan, Cambodia, Thailand, Laos, and Myanmar.
This image of an astronomical clock was designed by Hezekiah Conant of the US Patent Office in 1887. The top dial show the right ascension of the Sun and Moon. The two lower dials show mean solar and mean sidereal time. Published before 1923, it is in the public domain.