judy -
The actual celebration of these two holidays began on the night of Oct 31st, the evening of All Hallows Day, which was called All Hallows Even or Hallow E'en, now known as Halloween.
The beginning of celebrations now on the evening of the day before took place originally at the beginning of the day. The days began at the evening before. In the Orient it is still so; in Cairo you can buy evening papers with a date which we would consider as the date of the next day.
A trace of this usage you may find in Genesis I, 1 where every report of the creation on a certain day ends with: "It was evening, and it was morning: day one" (and so on).
The day began when the sun had set and it was really dark. That is why the Easter hare, Santa Claus, and the Xmas child (bringing the gifts in Germany) come in the night, i. e. as soon as the day has begun.
This leads to the question: When is it really dark? In the rabbinical tradition Sabbat begins when you can see three stars with one look, and Ibn-Hanbal, founder of an Islamic legal tradition, used a white and black thread. If you couldn't discern them it was dark enough for the beginning of a new day. (I used this device to stop my daughters' questioning when it is dark enough to light the tree on Xmas eve. I shall never forget how they cried: It's dark, I can't discern the threads any more, and I answered: Bad luck, I still can.)


Wilfried.