The third most powerful solar X-ray flare on record, a remarkable X17.2 category explosion, erupted from sunspot 10486 on Tuesday, 28 October 2003. This is the second largest X-ray flare ever seen by the ESA/NASA SOHO spacecraft, after the major X20 solar flare of April 2001. Regular observations of X-ray flares began in the 1970s. This explosion hurled a ‘coronal mass ejection’ (CME) almost directly toward Earth, which could trigger bright aurorae when the material reaches us in about a day. The Earth was immediately affected by intense X-ray radiation, which ionised the upper layers of the atmosphere, causing serious disruption to radio communications. The high-energy particles that followed (called a 'proton storm') could upset satellites by interfering with their electronics systems and damaging exposed components. During these storms, astronauts are advised to reduce exposure, particularly during spacewalks.
Our atmosphere protects people on the Earth, but passengers and crews on commercial jets at high latitudes could receive exposure equivalent to a normal medical chest X-ray. The CME associated with this flare is larger than the Sun itself and is one of the most dramatic halo CMEs ever recorded by SOHO. The material ejected by this CME is travelling towards Earth at 2145 kilometres per second (7.5 million km/h), as compared to a ‘normal’ speed for these events of 400 kilometres per second (1.5 million km/h). This is a very fast one! This image is from SOHO's LASCO coronagraph, a telescope that uses a disc to block the Sun's bright surface, revealing the faint solar corona, stars, planets and ‘sungrazing’ comets. In other words, a coronagraph produces an artificial solar eclipse.
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