Monitoring solar activity on the far side of the Sun from sky reflected Lyman alpha radiation

Solar active regions are known to be brighter in Lyman alpha radiation than the quiet sun. Accordingly, they illuminate more H atoms in interplanetary space through resonance scattering. As we show here, this excess of illumi nation related to active regions is clearly seen in full-sky Lyman alpha ma ps recorded by the SWAN instrument on board SOHO, including those excesses resulting from active regions which are on the far side of the Sun. Since s olar activity is most often connected to solar active regions, this techniq ue could be used in the future to improve the quality of Space Weather fore cast, by earlier detection of the birth of a new active region on the far s ide of the sun, before it comes into Earth's view at the East limb.