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n– 1719
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nThenAurora Borealis is another name for the Northern Lights—the dancingn“curtains” of light that sometimes appear in the night sky in thenfar north. (The same thing in Antarctic regions is called the AuroranAustralis.) n
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nOfncourse we know that this natural phenomenon had been seen many, manyntimes before 1719—by, for example, the many native peoples ofnAlaska and Canada—but for the English settlers in New England, itnwas a new and unexplained sight. Many witnesses in New England, onnthis day in 1719, saw a mysterious face looking back at them from thensky. Some responded with fright, thinking that this was a religiousnexperience foretelling the “last judgement.” n
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nOfncourse we know that this natural phenomenon had been seen many, manyntimes before 1719—by, for example, the many native peoples ofnAlaska and Canada—but for the English settlers in New England, itnwas a new and unexplained sight. Many witnesses in New England, onnthis day in 1719, saw a mysterious face looking back at them from thensky. Some responded with fright, thinking that this was a religiousnexperience foretelling the “last judgement.” n
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nNownwe know the true explanation: the sun not only emits light, but alsoncharged particles such as free electrons and positive ions. Thesenenergetic particles pour down on the surfaces of all the planets andnmoons, but because Earth has a magnetic field, the particles arenredirected and then funneled downward to the north and south poles.nWhen the particles collide with atoms in the upper atmosphere, thosenatoms emit light.
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nAurorasntend to get brighter whenever there are sunspots on the sun, becausenthese dark spots indicate solar magnetic storms that cause the sun tonemit more charged particles than usual. n
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Bynthe way, Earth acts like a giant magnet because of the rotation ofnits molten core. Venus, which is the closest planet to the Earth andnalso its twin in size, does not have magnetic fields. Scientist thinknthat Venus must have a iron core similar to Earth’s, but the planet’snvery slow rotation—one Venus day is 243 Earth days!—is just toonslow to produce the dynamo effect that causes Earth’s magneticnfields.
Bynthe way, Earth acts like a giant magnet because of the rotation ofnits molten core. Venus, which is the closest planet to the Earth andnalso its twin in size, does not have magnetic fields. Scientist thinknthat Venus must have a iron core similar to Earth’s, but the planet’snvery slow rotation—one Venus day is 243 Earth days!—is just toonslow to produce the dynamo effect that causes Earth’s magneticnfields.n
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nCannyou find out which other planets do or do not have magnetic fields?n(Hint: most of them do.)
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nAlsonon this Date:
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nBurkinaFaso’s Republic Day
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