There Goes the Sun

Natural History, June, 2001 by Richard Panek

Witnessing an eclipse today may not be the mystical experience it once was, but it's no less impressive.

What you'll see," one of the cruise ship's official guides was saying, "you won't be able to describe to your family. People cry. People scream. People babble." An unofficial guide--the director of a planetarium back in the States and one of our fellow passengers--had a more frankly romantic interpretation of what we were about to experience: "I equate it with love."

Can any natural event (even love) possibly live up to such advance billing? The passengers aboard a special cruise on the Black Sea in August 1999 were about to find out--as will people taking similar sea cruises or land expeditions in Africa this month, when the moon once again totally eclipses the Sun. Such an event isn't particularly rare. Unlike spectacular comets, which tend to streak into view only once or twice a decade, total solar eclipses occur on average about once every other year. What makes them seem so rare, however, is their inaccessibility.

You can witness the Moon precisely superimposing itself upon the Sun only if you happen to be in the right place at the right time. The right place--the path of the Moon's umbral shadow--is 170 miles across at its widest, and the right time--totality itself--can be seven minutes, thirty-one seconds at the longest and usually lasts several minutes less. A total solar eclipse will be visible at a given place on Earth only once about every 375 years on average, so if you want to see any of the three dozen or so such events that are going to occur during your lifetime, chances are you are going to have to go to it.

Which helps explain why eclipse cruises and land expeditions have become popular--and the best such tours not only get you there but also provide lectures and briefings on what to expect when totality arrives. That's not to say that the eclipse cruise I took in 1999 didn't have a casino or an onboard band featuring "The Gift From Ipanema" in its repertoire. Nor was every passenger "chasing totality," as eclipse veterans like to say: on the morning of the main event, fifteen passengers passed up the final and most extensive preparatory briefing in favor of a napkin-folding tutorial. Still, those of us who did go to the middle of the Black Sea for a good look at what some tour organizers were billing as "the last total solar eclipse of the millennium" found ourselves trying to get the most out of our two minutes and twenty-one seconds.

Among the phenomena any observer of a total solar eclipse can anticipate are

Weather. After the edge of the Moon meets the edge of the Sun, the temperature may begin to drop noticeably. Aboard our ship, idling in the August heat of the Black Sea, it fell 21 [degrees] F altogether, to 83 [degrees] at totality.

Shadow. Just before the beginning of totality, the shadow of the Moon will visibly race across the landscape--in our case, the calm surface of the sea--from the west.

Baily's beads. When the last rays of the Sun poke through the valleys along the perimeter of the Moon's disk, they create an effect that nineteenth-century British amateur astronomer Francis Baily described as "a string of bright beads."

Diamond-ring effect. The final Baily's bead appears together with the visible band formed by the solar corona.

Wildlife. Birds and beasts will be responding, perhaps starting to bed down for the "night" as the sunlight dims. But the response of human beings will be no less notable. As my fellow cruise passenger Robert J. Bonadurer, director of the Minneapolis Planetarium, said, "You can tell yourself that you don't believe the world is going to come to an end--but you do. And then you understand people shooting arrows at the Moon."

To be sure, a total eclipse of the Sun is not without its scientific applications, whether it's Arthur Eddington using photographic images of the 1919 eclipse to help validate Einstein's general theory of relativity or today's astronomers monitoring the event to view the corona, the highly ionized gases surrounding the Sun. But the psychological impact of seeing the perfect fit between Moon and Sun--the only such coincidence visible from the surface of a planet in our solar system--is what casual observers remember.

They'll be watching this month (see "The Sky in June," below, for details). And if you need any evidence that the impact of a solar eclipse is more psychological than scientific, consider what happened on our cruise immediately after totality. As the sight of the Moon creeping across the Sun--the spectacle that minutes earlier had awed everyone--continued to play itself out, only in reverse, hardly anyone paid attention. The band resumed playing; the totality chasers drank champagne and danced. Off to one side, Anthony F. Aveni, professor of astronomy and anthropology at Colgate University and one of the official onboard experts, noticed that our ship as well as several others in our immediate vicinity were already barreling back across the Black Sea. "We're all heading for the Bosporus," Aveni laughed. "We've abandoned the midline. What a bunch of eclipse hypocrites we are!"