All Purnima Tithis are considered auspicious in India. Vaishakha Purnima, Magh Purnima and Kartik Purnima are considered important as during these months one goes for shahi snana ( holyu bath) in Sun every day and covers the annual quota for Vitamin D. The consumption of Til during these days supplies the required calcium.

Buddha Jayanti falls on Vaishakha Purnima day. Gautam Buddha gained enlightenment at Bodhgaya under a pipal tree on Vaishakh Purnima and on the same day he attained Nirvana at Kushinagar.

People worship Lord Satyanarayana and observe Satyanarayana fasting on Purnima day. On this day of fast one is supposed to have oneness in spoken language, thoughts and actions.

1. Purnima is the day with high tides in the ocean
2. The body retains water during this day
3. On Ikadashi, people often observe water fast to neutralize the water retention during Purnima
4. Vaishak Purnima, is a special day for sun bath with Shreyat and Krishna til containing water.
5. According to the Bhavishya Purana, Lord Vishnu took is worshipped in turtle form on Vaishakha Purnima.
6. Turtle signifies withdrawal of senses. The fast on this day involves not speaking lie and withdrawing all sensual pleasures
7. This is considered rare and an extraordinary event. That is why Buddha Purnima is celebrated on Vaishakh Purnima every year.
8. Vaishakh Month is considered to be the ideal month to perform charity, homas, fasts etc.
9. Mantra: Om Namo Bhagvate Vasudevaya Namah.
10. Providing a thirsty person with water on this day is equivalent to performing a Rajsun Yagya.

(Disclaimer: The views expressed in this write up are my own).