UV Telescope Reveals Sun's Far Side

PARIS, France, June 29 -- Scientists say that they now can peek around the Sun and predict whether solar storms on its far side will shortly appear on the side facing the Earth, thanks to an UV telescope aboard a European spacecraft. The Solar Wind Anisotropies, or SWAN, is a telescope on board the Solar and Heliospheric Observatory (SOHO) -- a joint ESA/NASA project launched in December 1995 -- that can map the whole sky in ultraviolet light, a feat impossible from Earth, where the atmosphere completely filters short-wavelength UV rays. A European team of scientists headed by Jean Loup Bertaux of France's CNRS Service d'Aronomie has developed a technique using SWAN's UV mapping capabilities to infer activity taking place on the back side of the Sun.
According to the researchers, radiation from the Sun blows a bubble about one astronomical unit across in the huge cloud of interstellar hydrogen gas in which the solar system is embedded. The bubble's inside surface forms a sort of movie screen. When radiation from active solar regions hit the screen, the hydrogen gas begins to glow and UV hot spots are formed. Because the hydrogen bubble is so large -- bigger than Earth's orbit in some directions -- it is possible for SWAN to see hot spots caused by active regions on the far side of the sun, simply by looking at the part of the sky facing that side of the sun.