Tuesday, February 02, 2010

Looking for shadows

In the American news this morning you will read about Punxsutawney Phil, the famous Pennsylvania groundhog that will or will not see his shadow when he emerges from his burrow today. If he does, we are in for six more weeks of winter. If it doesn't, we can put away the parkas and welcome spring.

The fat woodchuck is part of a web of solar lore with roots in prehistory. Phil presides at the year's first "cross quarter" day. The fuss that attends his emergence from his burrow is connected to the Sun by more than a shadow.

The story begins 4 1/2 billion years ago in the chaos of the pre-solar nebula from which the solar system was born.

In a corner of the Milky Way Galaxy, a vast cloud of dust and gas began to contract under the influence of gravity. As the cloud got smaller, it spun faster, as an ice skater spins faster as he draws his arms close to his body. As the cloud spun faster, it flattened out, like a mass of spinning pizza dough.

This whirling pancake of dust and gas became our solar system. Most of the material was pulled to the center to form the Sun. Other whirling eddies within the cloud were collected by gravity to become planets. There was considerable chaos within the cloud. When the third planet from the sun settled into place, its spin axis had a tilt of 23 1/2 degrees to the plane of the pancake.

It was the luck of the draw. It might have been 30 degrees. It might have been zero.

If it were zero, no Punxsutawney Phil.

As the Earth revolves in its annual orbit, sometimes the northern hemisphere is tipped towards the Sun, sometimes away. In the first instance, the Sun's rays fall more directly upon the surface and heat it efficiently: our northern summer. In the latter case, the sun's rays shine obliquely and spread their energy more diffusely: winter.

If there had been no tilt, there would be no seasons. Climate, yes -- poles cold, equator hot -- but no seasonal variation. But there was a tilt, and the waxing and waning of the Sun's warmth and light was the central fact of life for our ancestors.

The bonfires of St. John's Eve, June 23rd, which are still lit in some parts of Europe, celebrate the Sun's ascension to its highest point in northern skies. Likewise, the winter solstice, when the Sun stood lowest, was marked with feasts of light to ensure the Sun's return. These ancient rites linger in the Christian feast of Christmas and the Jewish Hanukkah.

The equinoxes, when the Sun is halfway between its extremes of strength and weakness, were celebrated too. The spring equinox retains a place in our calendar through its connection with the Christian feast of Easter, or alternately, as the Ides of March or St. Patrick's Day. Celebrations of the fall equinox have slipped from prominence.

The cross-quarter days, midway between the solstices and equinoxes, are less familiar, but they too figured in ancient rites, and also lurk in our traditions.

The first cross-quarter day should mathematically fall about Feb. 4th or 5th. This became Candlemas Day, Feb. 2nd, in the Christian calendar. An old European rhyme asserts:
If Candlemas be fair and bright,
Come winter, have another flight.
If Candlemas brings clouds and rain,
Go, winter, and come not again.
Some Europeans looked for the shadow of the hedgehog on Candlemas. German immigrants brought the tradition to Pennsylvania and substituted the American woodchuck.

Punxsutawney Phil bears a weight of tradition on his fat, furry shoulders. His contrived appearance may seem inconsequential, a bit of local fun for the folks of Punxsutawney, but it is good that the old traditions live on in secular form to remind us of our common humanity on the tilted third planet from the sun.

(By the way, we celebrate the second cross-quarter day as May Day. The third cross-quarter day, which falls on or about August 7th, was perhaps remembered in the Christian calendar as Lammas, or "loaf-mass," a harvest feast, but it has vanished from our attention. The fourth cross-quarter day remains prominently with us as Halloween.)