SUNSPOTS ON THE FAR SIDE OF THE SUN can be detected through helioseismic holography, a process in which the sound waves that rumble through the body of the sun are slightly distorted when they reflect from the magnetically active regions around sunspots. In March of 1998, data from the orbiting Solar Heliospheric Observatory (SOHO) were processed with an algorithm that deduces the locations of those out-of-sight sunspots. Charles Lindsey and Douglas Braun of the Solar Physics Research Corp. report that their calculations of presumed sunspot positions on the far side of the sun correlated well with actual spots that later swung into view (revolving along with the sun on its 27-day rotation).

The researchers expect that eventually this method will be able to give valuable advance warnings of the type of space storms that arise from the solar flares and coronal mass ejections associated with the active regions on the sun's surface. Predicting "space weather" in the Earth-sun environment is important since astronauts' lives, the survival of satellites, and the stable operation of terrestrial power grids are tied to the particles and radiation that comes rushing at us from the sun. (Lindsey and Braun, Science, 10 March /pnu/2000/.)