Autumnal equinox today heralds shorter days

By: PHILIP K. IRELAND - Staff Writer | Wednesday, September 21, 2005 8:33 PM PDT ∞

CARLSBAD ---- For a few hours this afternoon, some say, it will be possible to stand an egg on end thanks to the exact balance between night and day.

Today is the autumnal equinox, the first day of fall. What that means is that at 3:22 p.m., night and day will be precisely equal, each exactly 12 hours long. Flagpoles, people, and buildings on the equator will not cast a shadow.

The coming days will grow shorter and cooler, and the nights longer and colder as the Earth turns toward the winter solstice on Dec. 21, the longest night of the year and the first day of winter.

The autumnal equinox has an opposite called the vernal equinox. On that day, March 20, 2006, like today, the length of day and night will be equal. Likewise, the winter solstice has an opposite, too. Called the summer solstice, June 21, 2006, will be the longest day of the year.

Hence, the four seasons are marked by these four celestial dates.

The physics of the equinox are complex, said Graham Oberem, a professor of physics at Cal State San Marcos.

In the simplest terms, the Earth is tilted on its axis 23.5 degrees. That tilt is what creates our seasons. The tilt remains fixed on a point in space ---- the North Star ---- as the Earth travels on its 365-day trip around the sun.

At the winter solstice, the Northern Hemisphere is tilted away from the sun, receiving less light during shorter days and longer nights, and the light is less direct. The result is a cold winter of long dark nights and short days. A half-year later, the opposite is true. The Northern Hemisphere is closest to the sun and the receives more direct sun for longer periods. Hence, the lazy days of summer.

The ancient Mayans, the Egyptians, the people of Ireland and Britain built precise stone structures to helped them track the seasons. Stonehenge in Britain, Chichen Itza in Mexico, and Mystery Hill in New Hampshire are all ancient megalithic sites that served as stone clocks.

Oberem said modern-day people can create the same effect with a nail and a piece of paper. A paper plate works well, too. Run the nail up through the center of the plate and place it outside in the sun. Each hour make a mark at the end of the nail's shadow. Only on the two equinoxes will the marks align to form a straight line. Try the same experiment in another month and the line will be curved, showing the change in the sun's path across the sky.

Rica French, an astronomy instructor at MiraCosta College, suggested noting the location of sunrise on the horizon each morning. Although most people think the sun rises in the same place in the east every day, the location changes slightly as the days grow shorter.

The autumnal equinox is a traditional time of celebration. The Chumash of Southern California celebrate the fall equinox sun ceremony during their month of "Hutash" after the harvest is picked, processed and stored.

Ancient Celts called Druids conducted a mock sacrifice of a large manlike figure made of wicker wood representing the vegetation spirit during the fall equinox. The practice has been reborn as the Burning Man Project in the Nevada desert.

Throughout history, humanity has been fascinated by the movement of the Earth and stars. Those little-understood concepts have formed the basis for many religions and their beliefs.

It is such belief that has helped the myth of egg standing at the equinox to survive. But in fact, it's bunk, according to national egg-standing expert Phil Plait, publisher of www.badastronomy.com. Plait debunked the wives' tale by taking a decidedly scientific approach. He tried and succeeded in standing eggs on end throughout the year.

In short, he says, anyone who does succeed in balancing an egg had a steady hand, a flat table and patience, and it had nothing to do with anything involving astronomy or physics.

Contact staff writer Philip K. Ireland at (760) 901-4043 or at pireland@nctimes.com.