Three solar flares erupted on the sun starting Tuesday, and the strongest electromagnetic shocks were being felt Friday by the ACE spacecraft, a satellite that measures radiation bursts a few minutes before they strike Earth, said Joseph Kunches, a scientist at NOAA's Space Weather Prediction Center in Boulder, Colo. Tom Bogdan, director of the center, said the sun is going from a quiet period into a busier cycle for solar flares and an increase in the number of such blasts is expected over the next three to five years.