Exact date of Buddha's death

Question : (Unedited)

Dear Sir,
I happened to learn that the exact date of Buddha's death is not known even though we commemorate it on a certain fixed date of the year. Why is there a debate on this one? Is it because people in the past were not that intelligent to keep track of events and modern scientists are more advanced?

I want to know the date that is mostly accepted and any shortcomings of the scientific researches performed on this, if any.

Thanks in advance

My comment:

Hi Ch,

Thank you for asking me.

The day is called "Wesak Day" or "Buddha Day". 　It is the thrice sacred day of the birth, enlightenment and passing away (parinibbana) of the Buddha. 　At the sixth World Conference of the World Fellowship of Buddhists (WFB) held in Phnom Pehn, Cambodia, in 1961, the conference resolved:
"That the first full moon day of May be recognized as the 'Buddha Day' and celebrated accordingly." 　The month of May corresponds with the month of Visaka of the Indian calendar. 　It was in the full moon day of Visaka that the thrice blessed events took place.