Monitoring solar activity on the far side of the Sun from sky reflected Lyman α 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 illumination related to active regions is clearly seen in full-sky Lyman alpha maps 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 solar activity is most often connected to solar active regions, this technique could be used in the future to improve the quality of Space Weather forecast, by earlier detection of the birth of a new active region on the far side of the sun, before it comes into Earth's view at the East limb.