To properly grasp this, you’ll need to consider leap year. Why we have it, what it actually is. Our calendar doesn’t function perfectly, you see, and leap year is necessary to occasionally–as in, every four years–adjust it. The ancients didn’t have leap years. With such being the case, there has, over time, been some “shifting” of dates. Halloween for us is October 31st. It is every year. Samhain (properly pronounced “sow-win,” I am told), however, the Celtic pagan celebration from which Halloween was born, did not follow a calendar. It was determined by a strict observance of the seasons. This year, the anniversary of the date on which the ancient Celts would have observed Samhain falls on November 7th. (That’s tomorrow, as I sit typing this article.)
It gets even more complicated, though, If we want to go by the stars, the Pleiades specifically, then Samhain doesn’t occur until November 20th or 21st. This linked article does a good job of explaining why this is. The important thing to take away from it, however, is that Halloween is NOT over, despite the fact that the department stores had employees tripping over themselves to clear the aisles of Halloween merchandise and start loading in the Christmas stuff early on the morning on October 31st. Those of us for whom Halloween is an entire season–for me it lasts from the first of October until Thanksgiving–were right all along.