Not that it hasn't happened before, said Crooker. Two hundred years of records showing the rise and fall in sunspot numbers suggest that there were other times when the sun was unusually calm, but we had no instruments in space then to make measurements, she said. In practical terms the most minimal solar minimum means it's a bad time for astronauts to venture to the moon or beyond, because they would be outside of the protective magnetic field of the Earth and more exposed to cell-damaging cosmic rays, said Crooker. It's about as bad, ironically, as a furiously active sun which spews out dangerous radiation that would also hurt astronauts beyond Earth's orbit. Either extreme is bad news for interplanetary travel. Inside Earth's magnetic field the main effect of the cooler, less windy sun is the cooling and lowering of the outermost part of the atmosphere. While that has minimal effects on the climate, it does slow down the rate at which orbiting manmade space junk gets dragged down and burned up in the atmosphere -- which is bad news to astronauts in orbit who fear collisions with the debris, Crooker explained. Ulysses is the only spacecraft to observe the sun in 3-D by flying over the sun's poles. The Ulysses mission has been underway for almost 18 years, allowing it to observe the sun during two solar minimums and one solar maximum. Related Links: |
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