Solar physicists have found an ingenious way to look at the far side of the sun. The discovery, announced in Paris on Tuesday at a meeting of astrophysicists, could lead to better forecasts of solar storms and other types of potentially destructive space weather.
The surface of the sun often erupts into solar flares and casts off strong gusts of solar wind. These blasts of fast, charged particles can wreak havoc with Earth-orbiting satellites, long-distance radio communications, and electrical power grids. To provide advance warning to satellite operators, who can put their equipment into a safe mode, the National Oceanic and Atmospheric Administration's Space Environment Center (SEC) in Boulder, Colorado, issues daily space weather forecasts. The forecasters scan the sun's horizon for active regions, which take about a week to rotate to the center of the sun's disk, where they are in a position to threaten Earth. "If we had a better idea of what's on the other side of the sun, we could give a much better long-term forecast," says space weather forecaster Chris Smithtro of the SEC.
Such advance notice may soon come from one of the 12 instruments aboard the Solar and Heliospheric Observatory, which observes the sun from a point 1.5 million kilometers from Earth. A group of researchers led by Jean-Loup Bertaux of the Service d'Aéronomie of the French National Center of Scientific Research in Verrires le Buisson used an ultraviolet all-sky camera, called the Solar Wind ANomalies (SWAN), to study solar UV radiation reflected and scattered by interstellar hydrogen atoms. Solar radiation sweeps the hydrogen out of the inner solar system, and the inner edge of the cloud, about the size of Earth's orbit, acts as a projection screen for UV rays from the sun. The team has now succeeded in observing the ultraviolet glow of an active region on the far side of the sun, about a week before the region had rotated into view. According to Bertaux, it's like seeing the beam of a lighthouse sweeping over the sea, while the lighthouse itself is out of view.
Such early views of the sun's far side could extend forecasts by up to 2 weeks--assuming they consistently predict solar disturbances. That much advance time would make preparations for countermeasures less hurried.