Christmas - The Flame and Tree

Excerpted from
The Physics of Christmas: From the Aerodynamics of Reindeer to the Thermodynamics of Turkey
By Roger Highfield

A tree festooned with flickering candles can be found on many Christmas cards, and for good reason. The evergreen and the candle celebrate the same thing: life-giving sunlight, an ancient symbol that dates back long before Prince Albert introduced the tree to Britain or Martin Luther supposedly first bedecked a tree with candles in the sixteenth century to remind children of the heavens from which Christ descended.

Our ancestors held winter festivities to usher in the annual return of sunlight, warmth, and fertility with rituals involving evergreens, which seemed to defy the cold winter months, and the yellow light of a living flame. Today Christmas and other seasonal celebrations, such as Kwanzaa and Hanukkah, are united by this latter symbol of the rebirth of the suns life-giving energy.

We can gaze deeply into the workings of the living world by studying what happens when we light a candle. The resulting flame marks the last step in an extraordinary series of physical and chemical processes that first capture sunlight to forge chemical bonds in wick and wax, then snap them to release the long-pent-up light

The most important of the processes is photosynthesis, a word derived from photo, meaning "light," and synthesis, meaning "the production of something." Photosynthesis drives the living economy that thrives on the surface of our planet. Each year green plants, including Christmas trees, harness the energy of sunlight to pluck 100 trillion kilograms of carbon dioxide from the sky, then combine it with hydrogen from water to build carbohydrates - their food - and to release oxygen.

One acre of Christmas trees can produce the daily oxygen requirement for eighteen people. In the United States there are approximately one million acres of growing Christmas trees; that means around eighteen million people each day are supplied with the oxygen generated as the trees harvest sunlight.

What is so beautiful about the act of lighting a candle on a Christmas tree is that it honors the cycles that turn within and without living things. The chemical energy generated by photosynthesis in plants is passed up the food chain, for instance, to grazing cattle and then on to a tallow candle. When the candle is lit at the gloomiest time of year, it releases this "cryptic sunlight", and returns the complex fat, or wax, molecules to the form in which the plants found them - water and a hot breath of carbon dioxide that can again be incorporated into living things.

The Christmas Tree

Like so many aspects of holiday celebrations, the roots of this symbol stretch back to prehistoric times, when ancient people became fascinated by how some trees and plants continued to thrive among the dead branches of a forest in winter. To a primitive mind in a deciduous world, an evergreen suggested permanence and a magical ability to endure with little help from the sun.

The ancient Egyptians brought green palm branches into their homes on the shortest day of the year, in December, as a symbol of life's triumph over death. This symbolism is also apparent in the Roman festival of Saturnalia, when buildings were decorated with evergreen branches of holly, pine, and ivy in honor of Saturnus, the god of agriculture.

Holly, ivy, and mistletoe are not only green but also bear recognizable fruit during the winter, again paying little heed to the elusive sun and keeping alive the hope that a fruitful year is to come. This triumph of fertility over the elements is echoed in the English legend of the Glastonbury thorn, planted by Joseph of Arimathea. The legend goes that soon after the death of Christ, Joseph went to Britain to spread the message of Christianity. Being tired from his journey, he lay down to rest and pushed his staff into the ground beside him. When he awoke, he found that the staff had taken root. The resultant bush was the Glastonbury thorn, which flowered each year on Christmas Day.

When discussing the prehistory of the Christmas tree, one also should take account of the Yule log, which was made from timber big enough to bum throughout the longest winter night, again to help usher in the return of the sun. The resulting ashes supposedly had the power to protect a house against lightning, to cure maladies, and to fertilize fields.

The use of the fir as a Christmas tree started in ancient times in the Black Forest in southwestern Germany, where evergreens and small trees were part of the winter solstice festival of pagan tribes. But it is not known when the fir, or Tannenbaum, was adopted in other parts of the country. Legend has it that Martin Luther (1483-1546) was so moved by the brightness of the millions of stars on a winter's night that he set candles on his tree to simulate the effect. However, the idea of a decorated tree dates from much earlier, being reminiscent of tree-dressing rituals, which can be found from Russia to India in forms such as Yggdrasil, the Nordic tree of life, the Indian Bodhi tree; and Eden's tree of knowledge. In various pagan rituals, a tree was decorated to encourage the tree spirits to return to the forest so that it would sprout again, which of course it did every spring.