– 1780
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n Unlikenearthquakes and volcanic eruptions, scientists can make very exactnpredictions about where and when we can observe a solar eclipse.
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nYounprobably know that a total solar eclipse is when the moon blocks outnthe sun’s disc entirely, for some people on earth, for a short while.nBasically, the moon casts its shadow on the earth, and whoever is innthat shadow sees an eclipse. This only happens rarely, because thenline-up of sun-moon-earth isn’t usually exact—the moon’s shadownmisses the earth, usually, and there is no eclipse.
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nButnwe know a lot about exactly where the sun, moon, and earth arenlocated, and how they move, so we can predict where a solar eclipsenwill happen years in advance. n
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nFornexample, we know that there will be a total solar eclipse for peoplenliving along earth’s equator on November 13 this year, and on Marchn20, 2015, March 9, 2016, August 21, 2017, July 2, 2019, and Decembern14, 2020….plus more…including December 5, 2048, and August 28,n2994!!! Check out NASA’s eclipse website.
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| Samuel Williams made a mistake in math… |
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nLet’snget back to 1780…
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nOnnthis date in 1780, British soldiers were fighting the American armynin the Revolutionary War. Harvard professor Samuel Williams hadnpredicted the exact time and location of a total solar eclipse, butnthat location was behind enemy lines! So Williams asked Britishnmilitary to allow his expedition to set up observational equipmentnat Penobscot Bay in Maine. The eclipse, he explained, would takenplace between 11:11 in the morning and 1:50 in the afternoon.
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| This is what you see when the moon only MOSTLY covers the sun. |
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nThenBritish generals graciously allowed the American astronomicalnexpedition safe passage, and the Americans set up at Islesborough,non Penobscot Bay. However, it turned out that the Williams’sncomputations weren’t exact enough—and, it turned out, thenscientists were in the wrong spot to experience the total eclipse!nInstead of covering the sun totally, the moon only covered MOST ofnthe sun.
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| The sun’s corona |
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nThat’sna bummer, because it is only when the sun is totally covered by thenmoon that we can see the corona—the thin outer atmosphere of thensun that is millions of degrees in temperature and very bright, butnwhich is normally invisible because the much brighter, much hotternsun drowns it out.
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nSonthe good news was that people put science ahead of warfare.
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nThenbad news is that someone didn’t check his math carefully enough, andnabout half of the hoped-for science wasn’t completed!
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nWendon’t necessarily need to say, “The moral to the story is, alwaysncheck your math,” because these days we use calculators andncomputers to do computations!
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nAlsonon this date:
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nPresident Teddy Roosevelt’s birthday
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nThree-Z Day in the Democratic Republic of the Congo
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