We have reached the season of spectacular change! The hottest days have passed, and each is shorter than the last. Groves on mountains take on brilliant colors. The State Fair is over, and school is in full swing. Everywhere, everyone seems more active and ready to get things done. Indeed, there is much to be done, for crops are ripe: It is the harvest season! The perfect time of year has come again, the time of change, for Earth has coasted through the equinox.

Here in the north it is autumn, while far to the south, across the equator, spring has arrived. It happens every year and we all feel it. Many enjoy it; others tolerate it, but few give much thought to what it brings.Sometimes it is difficult to think about riding on a great spinning ball of rock, with pockets of water, all surrounded by a wisp of gas, zooming round a star. For most of human history no such concept crossed the minds of tribes that would grow into nations. Obviously, it was the sky that moved. Anyone could see that the sun god leapt from sleep each morning to ride the sky and shower blessings down upon his children. Then stars moved about to beautify the night. We must be special, being at the center of all of this: nourished by warmth and light; refreshed by coolness and the beauty of a jeweled ceiling; given enough warmth, yet not too much.

It took no small effort to break age-old traditions, only a few hundred years ago: to dare to think new thoughts, formulate new theories that could be tested by observation and experiment, and to invent instruments that could expand our innate abilities to measure and perceive. The names of the scientific explorers loom large: Copernicus, Kepler, Galileo, Newton . . . the list goes on.

They made it easy to know the truth: Earth is a gyro whose spinning mass maintains the axis of its course. One pole points nearly toward a star, and so its name, "Pole Star." Each time it spins it carries sun, moon, planets and stars in review across our sky in the period called "one day." Each day begins at a slightly different place in space as Earth migrates along its orbit around a star, the sun. The orbit is tilted to the plane Earth spins in, and so different parts of the planet receive continually different amounts of energy. For six months, more and more of the northern hemisphere is bathed in the sun's rays until we reach the place where the northern hemisphere is tipped most toward the sun. Just the opposite is happening in the southern hemisphere. Then, for the next six months, in the other half of the orbit, the northern climes of Earth receive less and less direct rays until the tilting axis of rotation brings shade to the north pole and less direct rays to those of us within the northern temperate zone. Then, the south receives the more direct illumination of the sun. These ever-recurring changes repeat with each yearly orbit.

Watching from the surface of the spinning ball, we pace our activities by two waves that move constantly around the planet: We awaken with the wave of light, go about our work and play, then relax as the wave of darkness moves over us. Day after day it is the same, but not quite. Each wave of daylight comes at a slightly different place upon our horizons.

View Comments

Late last June, the northern hemisphere of Earth was turned as much toward the sun as the orbit permits: the solar-orb rose in the northeast, days were long and the sun passed high at the middle of the day to set in the northwest. Nights were as short as they could get. Then, slowly, as Earth moved on, the sun slipped southward in its rising and setting points and lower across the sky each day. Days got shorter and nights longer. Faster and faster the change occurred until we reached the time of equality between light and dark.

The maximum speed of change, the point of balance between day and night, was reached this year on Sept. 23 at 6:13 a.m. Mountain Daylight Time. So, yesterday the sun rose directly east, crossed our sky in the middle of its range, and set directly west. We felt its rays for 12 hours and lived without them for the other 12. At the poles of Earth the sun moved around at the base of the horizon, the north pole feeling its last solar rays until six months from now, and the south pole rejoicing in the returning sun to light its sky for months to come. Now, one day later, our portion of sunlight is a bit weaker, and so it will be until Dec. 22.

This is not cause for grief, for no matter the season, we do well to celebrate its gifts. Imagine, if you can, a planet that does not have rotation axis tilted to its orbit. Every day would be the same: half light, half dark, no seasons, very little change. Perhaps it is change itself that most deserves our revelry, for we are creatures of change. The best things we do, from birth to death, result in changes for ourselves and others. The Roman poet Ovid wrote, "There is nothing constant in the universe. All ebb and flow, and every shape that's born bears in its womb the seeds of change."

Each day brings adventure: new stars coming into view; new sounds in moving air. If you really think about it, you can almost feel the planet moving: rolling upon its axis; flying upon wings of the constant tug of gravity that binds us to a star.

Join the Conversation
Looking for comments?
Find comments in their new home! Click the buttons at the top or within the article to view them — or use the button below for quick access.