Some 2,000 years ago, on a holy night in Bethlehem as stars were brightly shining, a young woman gave birth to a baby and laid him in a manger. The baby Jesus was a thrill of hope for a weary world, the gospel story goes, and Christians ever since remember his birth in the candlelight of Christmas Eve.

Then, much more recently, though no one can seem to recall exactly when or where, came the birth of a new celebration. Adherents call it Christmas Adam. And they celebrate on Dec. 23.

Why? They have a universal reply:

“Because Adam came before Eve.”

It’s hard to define Christmas Adam, aside from the date. Unlike Christmas Eve, Christmas Adam is not part of an official Christian calendar. The Vatican certainly does not recognize it, and many churchgoers have not heard of it. There is not one way to celebrate.

But some evangelically minded and social-media-savvy Protestant churches and families have embraced the celebration, making up Christmas Adam traditions as they go, one joke at a time.

For some, Christmas Adam is purely a chance to share a clever pun. For others, it is practical way to compete in a crowded holiday season, by offering church services a day before the holiday actually starts.