X-ray images of active solar regions, photographed from Skylab, 1970s.
© National Aeronautics & Space Administration / Science & Society
Solar activity peaks roughly every 11 years at what is known as the 'solar maximum'. The solar maximum is 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 acros, which form when magnetic field lines below the surface become twisted and protrude through the photosphere. They are closely asociated with solar flares, sudden, masive outbursts of energy which occur on boundaries between areas with opposite magnetic fields, and extend far into the Sun's atmosphere