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Mercury, Nov/Dec 1995 Table of Contents

by James C. White II, Middle Tennessee State University

(c) 1995 Astronomical Society of the Pacific

Daylight dwindling and cold spreading, winter's arrival used to bring anxiety to our ancestors. Let it be a time for you to become aware of the Sun's motion in our skies.

This Month's Project: Tracking the Sun's motion at the winter solstice

Ask a friend what comes to mind when you mention winter: cold, bitter winds, darkness. But what about fear? To our ancestors, this time of year was one of great anxiety because the Sun, the giver of life, was getting lower and lower in the sky. Would it drop below the horizon, never to return?

They observed, as we do today, the motion of the Sun from a point high in the summer sky to a point low in the winter sky. The Sun stops and reverses its motion at the solstices (from the Latin sol, "the Sun," and sistere, "to stop"). Without our knowledge that Earth is actually a ball tipped slightly onto its side and swinging through space around the Sun, ancient peoples conducted elaborate plays to convince the Sun to return to Earth and deliver them from the darkness of winter.

The Chumash, Native Americans who inhabited what is now California, relied on their high chief and his assistants to pull the Sun back to Earth at the time of the winter solstice. Striking his sunstick with a magic stone, the chief uttered an incantation intended to compel the Sun to return to its position high in the sky. Such ritual was just the beginning of two days and nights of ceremony and celebration for the Chumash. The Pekwin, or Sun Priest, of the Zunis in western New Mexico had the formidable tasks of predicting the winter solstice and calling back the Sun to Earth. And about 5,000 years ago, ancient Britons constructed an unusual tomb, now referred to as Newgrange, that overlooks the River Boyne in eastern Ireland. For a week before and after the winter solstice, light from the morning Sun slices into the darkness of the tomb and illuminates a large basin in its innermost sanctuary.

Today we know that the solstices are due to Earth's recline, and they are less frightening, though no less exciting. Part of the year, the Northern Hemisphere gets more direct sunlight than the Southern Hemisphere. Because the two hemispheres get their most direct sunlight at opposite points in Earth's orbit around the Sun, the seasons for the two hemispheres are reversed. Northerners sit preparing for their winter solstice on Friday, Dec. 22, while their friends south of the equator eagerly await their summer solstice -- of course, at precisely the same time as our winter solstice.

If you live in the Northern Hemisphere, look to the southeast at sunrise on Dec. 22 and you will see the Sun rise at its most southerly point of the year. At midday look due south to see the Sun hanging low over the southern horizon. Only six months ago, at the summer solstice, you saw the Sun high in the sky at midday. And at sunset, glance to the southwest for the most southerly sunset you'll see this year. In the Southern Hemisphere, you'll see the Sun at its highest, most northerly point, but otherwise the idea is the same.

If you make these same observations on Saturday, Dec. 23, you'll find the Sun rising and setting just a little farther north. Because the sunrise and sunset positions move very slowly at this time of year, to see their motion clearly you'll have to observe over a number of days or weeks. The Sun will continue its northward march until the summer solstice on June 20. Try to notice these changes in the Sun's position in the sky and along the horizon from day to day. Our distant ancestors depended on such observations for planting, harvesting, and survival. We, armed with calendars and watches, can relax, look, and marvel.

Observing Guidelines

Refer to the newspaper or call your local television station to determine the times of sunrise and sunset. It is important to make each observation from the same exact location. Choose a rock to sit on, place a chair in a spot and don't move it, or remember to stand in the same place. If you use a camera, locate your tripod at the same spot each day. Identify permanent features on the horizon -- hills, mountains, trees, buildings, and so on -- and use them to note the Sun's location. On your drawing, mark the Sun's position, noting the day and time. If you make a photographic record, be careful to keep up with the date and time of each exposure.

What to Do With the Observations

Please submit your completed report by Jan. 30, 1996 by email to 0002032694@mcimail.com or by regular mail to John Isles, Attn: Guest Observers, 1016 Westfield Drive, Jackson, Mich. 49203-3630. The selection committee will evaluate the reports and choose the Guest Observer for the May/June issue. If you are selected, we will request a photograph of you or your group to include in Mercury.

We hope we'll get reports from as many latitudes as possible, in both the northern and southern hemispheres. Having observations of a Sun approaching a balmy summer solstice, as well as those of a Sun approaching a frosty winter solstice, will demonstrate how Earth's tilted axis causes the seasons to differ north and south of the equator.

Send your comments and suggestions for future projects to James White at jwhite@physics.mtsu.edu or Department of Physics and Astronomy, Middle Tennessee State University, Murfreesboro, Tenn. 37132.

JAMES C. WHITE II is a professor in the Department of Physics and Astronomy at Middle Tennessee State University in Murfreesboro. His astronomical research focuses on cataclysmic variables. White writes a monthly astronomy column carried by newspapers in Tennessee. His email address is jwhite@physics.mtsu.edu.