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The great eclipse of 2006

Perhaps you have not noticed it, but there is a secret and growing brotherhood in our very midst. You might have overhead a group of its members at an amateur astronomy meeting somewhere, or perhaps just an innocent conversation over the water-cooler. And I can now count myself a member. We are the people who have witnessed a total solar eclipse, something that can not be done without becoming, well, a bit changed.

In the beginning, the eclipse was just an afterthought for me. I had been lured by a free trip to Egypt to serve as a "host" astronomer on an eclipse tour. I didn't need to be asked twice to take a trip to the Middle East; that was an area of the world I was aching to explore. And hey, there was going to be an eclipse too. Great.

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But I had no idea. Really, I hate to say this, but there's nothing like it. I had seen partial solar eclipses before, but now, I'm afraid, I just can't qualify those as real eclipse experiences. I can see why people get addicted to this stuff. The main topic of conversation before the actual eclipse was how many eclipses everyone had seen before, and as soon as we got our capacity to speak back, people were already planning how to get to the next one.

I'm not surprised I was a little over-awed. After all, the excursion had started with a thorough tour of ancient archeological sites. I exhausted my supply of superlatives the first day at the Great Pyramids, and didn't have anything decent left over for the Temple of Karnak or Abu Simbel. By the time we had trekked across the entire north coast of Egypt to get to the Libyan border (the best viewing site in Egypt), my head was already pretty full of wonders. Out past the town of El-Saloum, bedouins had been hired to put their tents up on the high, windy plateau where thousands of tourists were gathering. The town was under a huge security shut-down, which forced us to get to the site many hours before the eclipse began. We didn't have any problem finding our site, but we did have to kick a bunch of elderly German tourists out of our tent (squatters!). Once that had been settled, crates of high-performance camera and video equipment, so laboriously pushed through all the security checks (with a bit of baksheesh to grease the wheels), were pulled off the buses while the more territorial members of our tour rushed to claim their viewing sites. This actually provided a bit of drama, as we had been warned not to stray too far from our assigned area; there were probably live mines nearby. I had to keep pulling back a lovely and spry 80-something-year-old man who kept seeing interesting wild flowers over the next hill....

Even as the partial eclipse began, I had no idea what I was in for. A big cheer went up when "first contact" occurred; a tiny dent in the side of the sun. It would take another hour for the moon to move completely in front of the sun, and since there were no clouds or impending sandstorms to worry about, the suspense was purely pleasurable. And so we settled in. As everyone there knew, the sun is still eye-searingly bright even with only a sliver left uncovered. The sky does get darker as the eclipse progresses, but the human eye is very good at adjusting to slowly changing light levels. You don't so much notice the sky getting darker as the air getting cooler. Sunlight doesn't seem to have any warmth associated with it. And then, moments before totality, the universe seemed to unravel.

It's worth noting that total eclipses of the sun are one of the lovely and strange perks of living on the planet Earth. In terms of the solar system as a whole, they're really quite rare. A lot of things have to be just right in order to get one. Think about it: isn't it amazing that the sun and moon appear, at least under certain circumstances, to be exactly the same size in the sky? In reality, of course, the sun and the moon are nowhere near the same size. The moon is roughly one quarter the diameter of the Earth, while the sun is about 100 times larger than the Earth. Do the math, and that makes the sun about 400 times larger than the moon. But the sun is also much farther away than the moon; about 400 times farther away. Get it? The spacing of the moon and the sun are exactly right so that they appear to be the same size. And yes, that really is just a wonderful coincidence.

This situation wasn't always the case, nor will it be in the future. A billion years ago, the moon was much closer to the Earth, taking only 20 days to make one orbit. And it's also worth specifying that by "day" we mean 24 hours, back when the moon was closer; the Earth took only 18 hours to turn once on its axis. Over time, the moon is moving farther away while the Earth "day" is getting longer - and these two things are definitely connected.

The moon orbits the Earth once every 29.5 days, which is also the exact amount of time it takes the moon to spin once on its axis. Think about it: that's why we only see one side of the moon from Earth. The moon keeps the same face pointed toward Earth at all times, as it orbits us once a month. In a real way, you can think of the lunar "day" as being the same as a month. And this time, it's not a coincidence. It all has to do with tides. As the Earth and moon tug on each other gravitationally, both bodies get stretched out by the pull. Two tidal bulges are formed on opposite sides of the Earth. Since the Earth is rotating on its axis, the tidal bulges move over the surface of our planet each day, causing the oceans (and even the land to a lesser extent) to rise and fall. Now, it takes energy to drag a tidal bulge around a planet and billions of years ago, the moon lost out in this duel. Each time the moon had to drag its tidal bulges around, it lost a little of its rotational energy. The smaller of the two bodies, its spin around its axis was matched exactly to its orbit around the Earth. In other words, it got tidally locked to the Earth's rotation. But the Earth is still rotating freely: our day is still much shorter than our month. The same gravitational dragging is now happening to us, and each time we drag our tidal bulges around, our spin slows down a little too.

In the meantime, the Earth is also boosting the moon to a higher, farther orbit. If you drew an imaginary line connecting the centers of the Earth and the moon, our tidal bulges would be slightly off-set and not point directly at the moon. Our rotation keeps the bulge just a little ahead of the moon, which give the moon a gentle prod each time the tides come around, causing it to move slightly farther away from the Earth. And where does the energy come from for that? Sure enough, our own axial spin is slowing down and our day is getting longer. And yes, someday in the far future, the Earth will also be tidally locked to the moon and our day will be the same as our month, evening out at around 40 days. At that point, the more distant moon will be too small in the sky to block out the sun.

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Suffice it to say that these wonderful events won't be around forever. The thing that I didn't expect was how my instincts reacted to the eclipse. Yes, I know perfectly well what causes a solar eclipse, and there aren't any worries about a monster eating the sun or anything like that. But it's almost like the human mind wasn't really meant to deal with the sky going dark in the middle of the day. As darkness came in, I felt a real twinge of panic. The sky was really going dark! The stars were coming out! The horizon all around us became one continuous band of fiery "sunset." What followed was fastest four minutes of my life. After the last tiny bit of the solar surface was obscured and the lovely "diamond ring" effect darkened, I looked up to see a hole in the sky. At that moment, I realized that I had taken for granted what it meant to be part of this solar system. It always feels so steady here on the Earth. But as three large spherical bodies all moved into perfect alignment, I swear I almost could feel the Earth hurtling through space on its orbit. When the instinctual panic subsided, I felt a lovely sense of peace and joy. Seriously, I felt like I had just had a wonderful, two-hour massage. Then the light returned and I and several thousand other tourists were standing numbly on the Libyan Plateau trying to figure out what to say. But that's just it. There isn't anything to say.

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