The Science of Christmas


So Christmas is over for another year. Presents have been exchanged, huge mountains of food devoured, and a vast amount of alcohol consumed. Time to put the decorations back in the attic, throw out the tree (if its natural), and start the countdown till next Christmas. 363 days to go!

Christmas is full of traditions and stories, but have you ever wondered about some of the possible science behind each. I’ve been reading ‘The Physics of Christmas’, a book that takes a look at some of the science that could potentially explain Christmas’ well known tales, and I thought I’d share some of the insights from its author that goes a long way to explaining some of the questions you may have wondered about Christmas.

The Physics of Christmas, Roger Highfield

First up……

Why does Rudolf have a red nose?

Nearly everyone will have heard the song of Rudolf the Red Nose Reindeer- how one foggy Christmas Santa Claus turned to his shunned reindeer to light the way of the sleigh and gain the respect of his fellow reindeer in the process. But why would a reindeer have a red nose in the first place?

Maybe he had a cold, or maybe whilst Santa is eating cookies and drinking milk Rudolf is having a few drams outside. The reality could be more to do with a reindeer’s physiology, particularly in their nose. They have folded turbinal bones covered with blood rich membranes, which warm the air as the reindeer breathes in and cools the air as it breathes out, thereby reducing the loss of heat and water. However this also creates a welcome environment for bugs, particularly parasites, which could cause infection in the nose leading to swelling and redness. Poor Rudolf.


On a side note one common mistake is that all of Santas reindeer are male, whereas actually the opposite is far more likely to be true. Both male and female reindeers have antlers, with the male antlers becoming particularly impressive during breeding season – a time of high testosterone. However, once the season is over the males shed their antlers before new ones start to grow four months later, and this period just so happens to coincide with the festive season.

So this means all of Santas reindeer must be in fact female, or even worse Santa actually castrates his reindeer taking away the testosterone of the males in the first place. Maybe new verses are in order for Rudolfs song…

Why is Santa so fat?

Santa has to carry around millions of presents around the world every year, so you’d think he would get into shape to be able to have the strength to do so. However every depiction of Santa has him with a giant belly that looks like a big bowl of jelly.

The new image of Santa?

The answer to Santas rotund figure could lie in his DNA. Studies into genetics have revealed that a fault into the ob gene could lead to increased weight. Now the ob gene is the blueprint for a protein called Leptin, which is a hormone that tells the brain how much fat is deposited in the body and which plays an important role in the brains ‘stop eating’ message. It helps the body determine how much fat is converted into energy and how much is stored. So it stands to reason that Santa may have this fault in his ob gene, making him over indulge and eat more than his body actually requires.

There is a good chance that Santa’s obesity means he is also suffering from some form of diabetes.

What exactly was the Bethlehem star?

The Bethlehem star is usually described as a brilliant bright object that pointed the three wise men towards Bethlehem , before settling above the building that contained the new born baby jesus. Now this is a very unusual pattern for celestial objects to travel, so what could the object have been; a comet, a star birth, star death, a conjunction of planets, a hesitation in planetary orbit, a sighting of the then unknown Uranus?

The way to find out is to work out when Jesus was actually born. According to the bible Jesus was born during the reign of Augustus Ceasar in Rome, sometime between 44 B.C and A.D 14, and also the reign of King Herod, who died in the spring of 4 B.C. Herod also killed all the babies in or around Bethlehem who were two years or younger to try and prevent the coming of the King of the Jews, meaning Jesus was born at least two years before Herods death. This puts a rough timescale of between 7B.C and 4B.C for the birth of Jesus.


Now some very clever astronomers can work out what events would have occurred in the night sky during the time, and see if any coincide with the Bethlehem Star. The window of 7-4 B.C rules out Haleys comet which arrived at 12 B.C, or the conjunction of Venus and Jupiter in 2 B.C. The time period does fit in well with a hesitation in Jupiters orbit however. This is when a planet appears to ‘stop’ in the night sky before carrying on after a few weeks.

This occurs because of the relative position of the planets around the sun. The planets farther out in the solar system orbit around the sun more slowly than Earth. Because of this, Earth catches up and overtakes as it completes its own orbit, making the planets appear to move backwards in the sky for a moment before reverting to their usual progression. Jupiter appears to be stationary at each end of the loop.

So maybe the three wise men saw Jupiter in the weeks leading up to its first stationary point, which happened to coincide with them arriving at Bethlehem where it revealed the barn that baby Jesus was lying in.

The book continues into the science of snow, Christmas shopping, Christmas spirits, and the festive blues, and is a very informative read.

To paraphrase my primary school book talk endings, I really enjoyed it and I would give it an 8 out of 10. The things you take from school eh?

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