Saka Dawa is one of the most auspicious days of the Tibetan Buddhist year.
It is the celebration of Buddha Shakyamuni's birthday, enlightenment and parinirvana, (passing away). In Tibet, this essential holy day is celebrated, remembering the life story of the historical  Buddha and by offering prayers of praises.

According to Tibetan tradition, the day marks the anniversary of Buddha Shakyamuni's enlightenment and parinirvana on the full moon day of the fourth month of the lunar calendar.  
It's believed the karmic results this day are multiplied inexplicably.