Features: October 2008

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Flight from Germany en route to the North Pole intercepted the Moon’s shadow at 9:41:33 a.m. Greenwich Mean Time. During the brief “totality run” the aircraft flew northeastward, broadside to the Sun, to provide a view of the eclipse from the passenger windows on the right side (it being morning, the Sun was in the east)

Ian Worpole

As regular readers of my “Skylog” column are aware, a total solar eclipse was predicted for August 1, 2008, one whose track would stretch from northern Canada across the Arctic Circle and into Siberia and China. Although I had traveled to witness nine previous eclipses, I figured I would have to forego this one—hard to reach from my home base near New York City. Even a trip to Novosibirsk—a readily accessible major city in Siberia, directly in the path of the eclipse—didn’t seem worth the investment of time and money. The likelihood of clear skies there was little better than fifty-fifty, given the usual weather patterns at that time of year. But then, in late June, I was presented with an opportunity to observe the eclipse from a most unique vantage point.

Once or twice a year, a German tour company called Deutsche Polarflug runs a twelve-hour sightseeing flight to the North Pole and back. Their flight path scheduled for August 1 promised an unusual bonus: en route to the Pole, it would intercept the total eclipse, and the aircraft would be filled with scientists and inveterate eclipse chasers. When I was invited aboard to cover this event for Natural History, I readily accepted!

Total solar eclipses are a happy accident of nature. The Sun’s 864,000-mile diameter is fully 400 times larger than that of our puny Moon, which is 2,160 miles. But the Moon also happens to be about 400 times closer to the Earth than the Sun (the ratio varies a bit, as both orbits are elliptical), and as a result, when the orbital planes intersect and the distances align favorably, the new Moon can appear to completely blot out the disk of the Sun. On such occasions, the Moon is casting its dark, slender cone of shadow (called the umbra) upon the Earth’s surface; that shadow can sweep a third of the way around the Earth in just a few hours. Those who are positioned in the direct path of the umbra will see the Sun’s disk diminish into a crescent, while beneath that spectacle, the Moon’s shadow will be rushing toward them across the landscape. During the brief period of totality, when the Sun’s disk is completely obscured, they will be engulfed in an eerie semidarkness, quite different from the onset of darkness at the end of a sunny day.

Passengers take in views prior to the eclipse

Joe Rao

Self-evidently, the phenomenon differs from a total lunar eclipse. That is not only because in one case the Sun is obscured from our view, and in the other the Moon; rather, they are obscured in different ways. Astronomically speaking, a solar eclipse can be called an occultation: a masking of a celestial body by another that passes in front of it. During a total lunar eclipse, in contrast, the full Moon passes completely into Earth’s shadow. From another point of view—that of an observer on the Moon, for instance —a total solar eclipse amounts to a partial (very partial) eclipse of the Earth.

Contrary to popular belief, total solar eclipses are not particularly rare. Astronomers predict sixty-eight to take place during the twenty-first century—one about every eighteen months. That’s not counting annular or “ring” eclipses (in which the Moon is too far from Earth to completely cover the Sun, and the tip of the umbra doesn’t quite reach Earth’s surface); hybrid eclipses (which are annular along one part of the path, total along the rest); and a goodly number of partial solar eclipses.

But if total solar eclipses aren’t all that rare, seeing one is—mainly because (even assuming clear weather) you have to be at the right place at just the right time, and the Sun and Moon do not arrange their assignations for human convenience. The track traced by the Moon’s umbra on Earth can run for many thousands of miles, but it’s also very narrow, at most about 170 miles wide. It has been calculated that on average, a total eclipse of the Sun is visible from the same spot on Earth only once in about every 375 years. If you think back to a time when human societies were small and communications and transportation limited, not only were the chances of seeing a total solar eclipse slight, but the fact that anyone else had ever seen one would not be common knowledge. The phenomenon would have been regarded with awe and, likely, fear—as a sign that the gods were angry, an omen of impending disaster. Many people believed that the Sun disappeared because it was being eaten by a dragon. And, of course, as soon as the priests—the only astronomers (or rather, astrologers) of the earliest civilizations—were able to forecast such happenings, they could use their skills as a means to impress the multitudes.