This festival is celebrated by married women, Vata Savithri Poornima/Hunnime is a Hindu festival celebrated across the country. Since it is observed as an austerity it is also called as Vata Savithri Vratham. It is performed mainly for the good health, longevity and wellbeing of their spouse (husband).
While in North India it is celebrated on the New Moon day (Amaavaasya) of the lunar month Vaisakha maasam; in South India it is celebrated on the Full Moon day (Pournami) of the lunar month Jyeshta Maasam due to calendar difference that is being followed. There is also a tradition of performing this Vratha on Jyeshta Bahula Amaavaasya day. Whatever may be the date of celebration, legend behind this festival/Vratha is the same.
According to its legend the event dates back to Krutha Yuga and is assigned to and named after a chaste and virtuous woman called Savithri daughter of Ashwapathi who was King of Madra Desa. She married a person by name Satyavantha who was destined to die within a year of her marriage.
When her husband’s soul was about to leave his body, Savithri literally combated (implored and convinced) with Yama Dharmaraja the Lord of death with her sheer determination and devotion and wins back her husband’s life along with the lost kingdom. Thenceforth she came to be popularly called as Sati Savithri and in her name an austerity called Vata Savithri Vratham has come into existence.
Women observe fasting for three days starting from Trayodasi and ending with Pournami or at least on the day of Pournami during this Vratham. On the third day that is on the lunar day Jyeshta Sukla Pournami, married women specially worship the Banyan tree which is also known as Vata Vruksha or by planting a sapling of Banyan tree in a Thulasi plant by invoking Savithri as a Goddess with Shodasa Upachara Pooja and conclude the Vratham.
The austerity behind this festival, its significance and the story of Sathi Savithri is said to have been narrated by Sage Markandeya to Dharmaraja (eldest of Pandavas), Draupadi Devi and others during their Vanavaasa.
It is said and believed that those who read/listen to the story of Sati Savithri will be bestowed with prosperity and happiness in their life and women who observe this austerity will be bestowed with auspiciousness forever.
The episode of Savithri-Satyavantha forms a part of Pativratha Mahatmya in Vanaparva of the epic Maha-Bharatha.