How often do the 7 sisters. the full moon,and Oct 31-Halloween ,happen at the same time?

Answer 1

The chances of a full Moon falling on any particular day are about 1 in 29. If you consider that the Moon looks close enough to full for a day either side of that, you could up that to 3 in 29.

Not sure what you mean about the Seven Sisters (Pleiades). They will be in the sky every Halloween night, but a full Moon on Halloween would be about 25° away - close to, but certainly not in the Pleiades.

Answer 2

I believe that last year the full moon was on Halloween. I too dont know what you are talking about how often for the Pleaties. They are in the sky if that is what you mean.