Predicting Solar Eruptions
July 12, 2006 | If astronauts had been on the Moon in early August, 1972, they would have been at best terribly queasy, and at worst — dead. A burst of charged particles that suddenly erupted from the Sun would have caused severe radiation sickness, dosing any unlucky Moonwalkers with about 400 rem — almost 50,000 times the radiation dose you get from a chest X-ray. Fortunately, the burst, known as a coronal mass ejection (CME), erupted during the months between Apollo 16 and Apollo 17, so no astronauts were harmed.
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http://skyandtelescope.com/news/article_1754_1.asp