Black Hole Sun
(Originally published in Camping Life Magazine)
Comets may look like stars with tails, and meteors and meteorites look like stars falling from the sky, but they pale in comparison with the two most spectacular astronomical events we're likely to see - a total eclipse of the sun or moon. In fact, outside of the once-in-fifty lifetimes occurrence of a supernova so bright it can be seen in broad daylight, I don't think there's anything that really compares with the experience of seeing a total eclipse, especially the solar variety.
The bad news is that total solar eclipses aren't exactly a dime a dozen. Occurring only in a narrow path as the moon comes between the earth and the sun, total solar eclipses require either a lot of luck or a lot of planning to experience. For instance, the last total solar eclipse of the 20th century lasted only 2 minutes and 23 seconds, and was only visible over a swath of Europe, the Middle East, and India on August 11 of this year. There won't be another total solar eclipse visible ANYWHERE until December 4, 2002, and it will only be seen in Southern Africa, the Indian Ocean, and Australia, and even there only for 2 minutes and 3 seconds. With fewer than 70 total solar eclipses occurring each century, getting in position to experience totality can be a once-in-a-lifetime event.
The good news is that seeing a partial solar eclipse is a lot - a whole lot - easier. In fact, on December 25, 2000, those of us in North America will see a 72 percent eclipse.
Stop and think about that for a second. A solar eclipse, albeit a partial one, on Christmas Day of the year 2000. If that's not a scenario tailor-made for symbolic significance, I don't know what is.
The power of an eclipse, even one not on Christmas Day, on us is indisputable. The earliest record we have of an eclipse was written in China in about 2134 B.C., when the Shu Ching notes, "the Sun and Moon did not meet harmoniously." Nor did the eclipse and the careers of royal astronomers Hsi and Ho, who hadn't warned the emperor that an invisible dragon (or so it was then believed) would be eating the sun that day. The sun did return, but that was the end for Hsi and Ho, who were beheaded for their mis-forecast.
In an effort to avoid sharing the fate of Hsi and Ho, future astronomers set about finding ways to predict eclipses. Some believe that Stonehenge is actually an eclipse predictor, and there's evidence to support this theory. To predict eclipses, you have to know three cycles: annual, so you know when the year begins; lunar, so you know the phase of the Moon; and "nodal," which takes into account two invisible points in space where the Moon's orbit intersects the plane of the Earth's orbit. The first two cycles are pretty obvious, but to figure out the "nodal" cycle takes years of very precise observation. Still, by moving stones around a ring within Stonehenge to mark time, this cycle can be tracked.
We're a bit more advanced - or at least we like to think we are - than the people who built Stonehenge, but we still want to be able to predict eclipses. And we can. The details of such predicting are complicated, but we have been able to determine that whenever the new Moon appears within 18.75 days of a node (where the Moon's orbit intersects the plane of the Earth's orbit; there are two of these), there will be a solar eclipse. I won't go into the math here, but the eclipse cycle repeats every 18 years and 10 or 11 days (the vagaries of this are maddening), which makes it a breeze to pinpoint every eclipse that's coming, as well as every eclipse that's ever occurred.
The hard part is figuring out WHERE the eclipses are. Unlike the timing, the location of eclipses doesn't seem to follow any cycle, although we can predict location based on the positions of the Earth, Moon, and Sun well in advance. But if you plan on just standing pat and waiting for an eclipse to wash over you, you may be in for a letdown. On average, it looks like a given site will see a total solar eclipse every 360 years. But that's on average. In reality, London once went 837 years between total solar eclipses, while Angola, in Africa, will see totality on June 21, 2001, and again on December 4, 2002. Go figure. Better yet, go to Angola.
Knowing when and where eclipses have and will occur is invaluable to us because it allows us to date with some precision records of previous eclipses and get in position to see those in the future. For instance, in the Bible, Amos 8:9 says "'And on that day,' says the Lord God, 'I will make the Sun go down at noon and darken the earth in broad daylight.'" We know "that day" was June 15, 763 B.C. We also know that the war between the Lydians and the Medes ended when a solar eclipse on May 28, 585 B.C., scared both armies so badly that they gave up fighting. And, like I wrote earlier, we know that the next total solar eclipse will take place on December 4, 2002, and if you can get to Australia, you'll be able to see it. Good luck.
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