South and Southeast Asian solar New Year

The traditional New Year in many South and Southeast Asian cultures is based on the sun's entry into the constellation Aries. In modern times, it is usually reckoned around 14 April.

Origins
As most countries and cultures of South and Southeast Asia lie within the Indian cultural sphere, the development of their traditional calendars have been strongly influenced by some form of the Hindu calendar. As in many other calendars, the New Year was based on the northern hemisphere vernal equinox (the beginning of spring). However, the Hindu calendar year was based on the sidereal year (i.e. the movement of the sun relative to the stars), while the Western Gregorian calendar is based on the tropical year (the cycle of seasons).

In ancient times, the sun's entry into Aries coincided with the equinox. However, due to the earth's axial precession, the sidereal year is slightly longer than the tropical year, causing the dates to gradually drift apart. Today, the sun's entry into Aries occurs around 18 April, according to astronomical definitions. Some traditional calendars are still marked by the sun's actual movements while others have since been fixed to the Gregorian calendar.

The sun's entry into Aries is known as  in Sanskrit, and is observed as Mesha Sankranti and Songkran in South and South-east Asian cultures.

Celebrations
The specific New Year observances include:
 * In the Indian Subcontinent (South Asia):
 * Bohag Bihu: Assam, India
 * Bisket Jatra or Baisakh Ek Gatey: Nepal
 * Pahela Baishakh: West Bengal, east and northeastern India, and Bangladesh
 * Pana Sankranti: Odisha, India
 * Sangken: Khamti, Singpho, Khamyang, Tangsa in Arunachal Pradesh and Tai Phake, Tai Aiton, and Turung in Assam
 * Bwisagu: Bodoland region of Assam, India
 * Buisu: Tripura, India
 * Gudi Padwa in Maharashtra & Goa, India
 * Bizhu: Chakmas in Mizoram, Tripura, and Bangladesh
 * Ugadi: Andhra Pradesh, Telangana
 * Puthandu: Tamil Nadu and Puducherry, India, and northern and eastern regions of Sri Lanka
 * Vishu: Kerala, India
 * Bisu: Tulu Nadu region of Karnataka and Kerala, India
 * Jur Sital: Mithila region of Bihar, India, and Nepal
 * Vaisakhi: Punjab, north and central India; Nepalese New Year
 * Aluth Avurudda: Sri Lanka
 * In Southeast Asia:
 * Thingyan: Myanmar
 * Pi Mai: Laos
 * Songkran: Thailand
 * Choul Chnam Thmey or Moha Sangkranta : Cambodia
 * Water-Sprinkling Festival: Dais in Sipsongpanna in Yunnan, China