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Dec25 Fun Holiday – Grav Mass Day

Grav-Mass Day is an unofficial holiday celebrated annually on December 25, the birth anniversary of English physicist and mathematician Isaac Newton.

Apple floats with no gravity over a hand.

Newton credited the apple for the idea about gravitation.


A play on Christmas, the holiday is a celebration of science and reason. It is also considered to be a secular alternative to the Christian holiday.

Grav-Mass refers to the Gravitational Constant and Mass, two key components of Newton’s law of universal gravitation.

Science Fiction Origins

The holiday was the brainchild of computer programmer and Internet rights activist, Richard Matthew Stallman. He was however, not the first one to use the term grav-mass, also sometimes spelled as gravmass or gravmas. It is believed that it was first used in a short story called Merry Gravmas by science fiction writer, James Hogan.


A similar holiday called Newtonmas is also celebrated on December 25. Rumor has it that Newtonmas was first celebrated in 1890, 248 years after Newton's birth, by the members of Newton Association. These fans of Newton met for the first time at Imperial College and spent Christmas Day exchanging their ideas and thoughts about Newton's works and theories.

Sir Isaac Newton is one of the most significant scientists of all times. He was responsible for formulating the laws of motion and gravity, and along with Gottfried Leibniz, he is credited for inventing the field of calculus. In addition, Newton worked extensively in the fields of optics and alchemy.

How to Celebrate?

  • Celebrate the life and times of Isaac Newton by sharing scientific ideas and discoveries with each other.
  • Stallman, the inventor of the holiday, recommends decorating one’s Christmas tree with apples – the fruit that Newton credited for giving him the idea about gravitation.
  • Make science and physics related parodies of Christmas carols and sing them.
  • Greet people by saying "Merry Grav-Mass to you", and respond by saying "may the Force be proportional to your acceleration". These greetings come from Hogan’s short story.
  • Send Grav-Mass Day greeting cards that say "Reasons Greetings to you".

Did You Know…

…that technically we should be celebrating Newton's birthday on January 4? This is because when he was born on December 25, 1642, the Julian Calendar was still in effect in England. This date converts to January 4, 1643 in the Gregorian calendar.

Grav Mass Day Observances

Fun Holiday: Grav Mass Day Observances
2024WedDec 25Grav Mass Day
2025ThuDec 25Grav Mass Day
2026FriDec 25Grav Mass Day
2027SatDec 25Grav Mass Day
2028MonDec 25Grav Mass Day
2029TueDec 25Grav Mass Day
2030WedDec 25Grav Mass Day
2031ThuDec 25Grav Mass Day
2032SatDec 25Grav Mass Day
2033SunDec 25Grav Mass Day

See all Fun Holidays

Other Fun Holidays around December 25

23 Dec


Celebrate this unofficial holiday created by the makers of the comedy TV series, Seinfeld with feats of strength and the airing of grievances.

24 Dec

Eggnog Day

Make a pitcher full of eggnog (or egg nog) to stir up the holiday spirit.

26 Dec

Thank You Note Day

Write thank you notes to everyone who had been kind to you during the year.