X-ray image of active regions on the Sun, photographed from Skylab, 1970s

X-ray image of active regions on the Sun, photographed from Skylab, 1970s. Solar activity peaks roughly every 11 years at what is known as the 'solar maximum', characterised by a heightened level of sunspot activity and other related phenomena such as solar flares. The active regions occur due to intense magnetic fields which rise to the Sun's surface, the photosphere, from deep within its interior. This results in the formation of sunspots, relatively cool areas up to 50,000 kilometres across, which form when magnetic field lines below the surface become twisted and protrude through the photosphere. They are closely associated with solar flares, sudden, massive outbursts of energy which occur on boundaries between areas with opposite magnetic fields, and extend far into the Sun's atmosphere. ©SSPL/NASA