Mesha Sankranti, also known as Maha Vishuva Sankranti, as per Vedic astrology, is the day when the Sun enters Mesha Rashi or Aries Zodiac. In most of the Hindu Solar Calendars this day signifies the beginning of the New Year.
The Solar calendars followed in India including Tamil, Malayalam, Oriya and Bengali Calendar follow different rules to mark the first day of the year based on exact time of the Mesha Sankranti. As per the Oriya Solar calendar, New Year Day is taken as the same day as the Sankranti, if it happens before Hindu midnight. In Orissa, Mesha Sankranti is celebrated as Pana Sankranti.
As per Tamil Calendar, if Sankranti occurs after sunrise and before sunset, the same day is considered as New Year day. If Sankranti occurs after sunset, then the year begins on the next day. Tamil Nadu celebrates Mesha Sankranti as Puthandu.
According to Malayalam calendar in Kerala, the day between sunrise and sunset is divided into five periods. If Sankranti occurs within the first three of them, then the year begins of the same day; otherwise it begins on the next day. That means, if Sankranti occurs within Madhyahna, the same day is observed as the New Year Day; otherwise it will be observed on the next day. In Kerala, Mesha Sankranti is celebrated as Vishu.
According to Bengali Calendar, if Sankranti occurs between sunrise and midnight of the day, then the year begins on the following day. If Sankranti occurs after midnight, then the year begins on the next day. In West Bengal Mesha Sankranti is celebrated as Naba Barsha or Pohela Boishakh.
In Assam, Mesha Sankranti is celebrated as Bihu and in Punjab it is celebrated as Vaisakhi.
Above rules hold good for calculation of the New Year day. However, for calculation of auspicious time for performing rituals, pujas and Dan-Punya activities related to Sankranti, the above rules are not sufficient. Calculation of the exact moment of Sankranti is a must, because some specific time duration exists before or after the Sankranti moment, which is considered most appropriate to perform Sankranti related activities.
In case of Mesha Sankranti, ten Ghatis before and ten Ghatis after the Sankranti moment are considered auspicious and hence this time window should be followed for all Dan-Punya activities. If Sankranti takes place after sunset but before midnight, then the second half of the day is considered; and if Sankranti occurs after midnight, then first half of the next day is considered auspicious for Mesha Sankranti rituals.
Sankramanam is the other name for Sankranti in South India.