Powerful solar flare, SOHO spacecraft X-ray image. This flare (right), which erupted on 7th September 2005, was rated as X17, making it the 5th strongest ever recorded at the time. Flares of this strength, if directed towards Earth, can knock out satellites and cause blackouts and widespread displays of aurora (northern and southern lights). This flare was not directed at Earth, however. Flares occur when energy released in twisted magnetic fields above sunspots is released. This flare was associated with the sunspot 798. This sunspot group caused several other flares in September 2005, making it the most active solar month since March 1991.