December 25 is the birthday of Isaac Newton. On this day, we celebrate the existence of comprehensible physical laws and we call it Newtonmas or Grav-mass.

The name Newtonmas can be attributed to The Skeptics Society, which needed an alternative name for its Christmas party.

Celebrants send cards with “Reason’s Greetings!” printed inside, and exchange boxes of apples and science-related items as gifts. The celebration may have had its origin in a meeting of the Newton Association at Christmas 1890 to talk, distribute gifts, and share laughter and good cheer.

One other way to celebrate Grav-mass is to decorate a tree with apples and other fruits. Glue them or attach them, but not too well! The idea is that occasionally a fruit should fall.

Another way to celebrate Grav-mass, in a group, is by telling each other about scientific knowledge and understanding, or discussing what kind of experiment could answer an unresolved question about the world.

Newtonmass can be celebrated by anybody who loves science and wants to have a reason for a celebration. It’s not exclusive to any specific group or belief.