I’m looking forward to this solstice for another reason altogether: the 14.9 hours of sunshine that we’ll get on that day. In fact, this will be my first summer solstice in a year and a half. Enduring two winters in a row, a downside of my sabbatical down under, was much tougher than I ever would have thought. I can say honestly that these long sunny days are now very much appreciated by all of us in the Miller family.

Near the end of the second winter though, I did get a chance to escape to the sunny Southwest US. There, sun observing has a long tradition. For instance, atop a mountain on the Tohono O’odham Indian Reservation sits Kitt Peak National Observatory. Along the southeast ridge, two solar telescopes are perched 4,000’ above the surrounding terrain.

The McMath-Pierce solar telescope has the distinctive triangular shape of a fallen-down number seven. In fact, half the telescope is underground, and it’s the only telescope that I’ve ever literally walked inside on a tour! At the apex sits three flat mirror heliostats, the largest being 2 meters across, to send light deep inside the telescope. Football-field sized focal lengths result in superb resolution. Beside the McMath-Pierce is the Solar Vacuum Telescope. The light path is evacuated: without air to heat there is no turbulence to degrade the solar image.

Casa Grande Ruins, may be another solar observatory you can walk around, even if not actually in. The ruins of the Great House, now protected under a steel canopy, are oriented almost perfectly with the compass directions. Sunrise or sunset beaming through a window on the eastern or western side reaches it’s greatest excursion on the opposite wall at the solstices, and thus can be used to set that date. The geometry works out, but no one really knows if the Hohokam actually used sunbeams to mark their calendars. 

Even more mysterious are the petroglyphs found at many sites all over the southwest US. Some are animal or human forms and seem to relate to hunting and gathering food. Others are more geometrical or even abstract. Crescents and stars surely relate to the sky, but what of these spirals? Could they too relate to the Sun’s seasonal movements and represent a calendar?

Today, we can predict the seasons with precision, so we have no need for solstice markings except as garden ornaments. Nevertheless, the sun is still fascinating, whether doing science with a mountain-top world-class telescope, observing sunspots from your backyard telescope, or just keeping a lookout for heightened auroral activity. But for me? Pass the sunblock.

Doug is indeed fortunate that his day-job’s fieldwork often takes him to the sunny beaches of the Delaware Bay. Moondark is written by Doug Miller, published on the web , and printed in the Delmarva Star Gazers' Star Gazer News and the Delaware Astronomical Society's FOCUS. Please address comments and suggestions to dcmiller@dmv.com. This document was last revised on 23 May 2001. All text and images copyright © 2001 Douglas C. Miller, All Rights Reserved. This material may not be reproduced in any form without prior permission.