Behind the active Sun

The Sun rotates rapidly, with an equatorial period of 27 days, and magnetic active regions can appear suddenly on the eastern solar limb as the Sun turns. These can generate huge solar flares or coronal mass ejections, triggering space weather events that can negatively affect the Earth. Many such events could be anticipated a week or more in advance if we could effectively view the far side of the Sun. Helioseismology can do this; it allows us to monitor the evolution of large active regions throughout their lifetimes and to forecast their arrival before they rotate onto the Sun’s near side.