A solar flare is a sudden and very powerful burst of magnetic energy occurring on the surface of the Sun. Solar flares occur when the Sun´s magnetic fields reconnect at the site active regions known as sunspots, ejecting clouds of electrons, ions and atoms into space. The radiation is emitted at all wavelengths of the electromagnetic spectrum. Large flares can emit energy ten times greater than the energy released by a volcanic eruption. The most powerful solar flares, which occur when the Sun reaches it solar maximum, can interfere with radio communications, cause blackouts and give little doses of radiation to people flying at the poles.
Solar flares are classified based on their strength as A, B, C, M, and X. Each letter represents a considerable increase in energy output, corresponding s to ten times more energy than the preceding letter. Within each class there is a finer scale from 1 to 9, so that an X2 flare is two times more powerful than an X1 flare. A, B and C flares are too weak to affect Earth; however, M and X flares are most often related to a number of effects on the Earth, including current surges in electrical lines, damaging radio communications and satellites
The frequency with which solar flares occur coincide with the Sun´s eleven year cycle. During a solar minimum, the active regions (sunspots) are rare and only few solar flares are detected; however, sunspots increase as the Sun reaches its maximum. Massive solar flares are associated with coronal mass ejections (CME) which can produce geomagnetic storms, affecting radio communications, electric power and low orbiting satellites and endanger astronauts working in space. These energetic particles cause the glow of auras on the Polar Regions as well.
Solar flares are detected using specialized scientific equipment. The radio and visible emissions of the spectrum can be observed with telescopes on Earth, however, the more energetic emissions, including X-rays and gamma rays emissions require the use of high technology observatories situated in space, such as the Solar and Heliospheric Observatory (SOHO) which employs 11 instruments to study the Sun, including the Extreme Ultraviolet Imaging Telescope (EIT), the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) and the Ultraviolet Chronograph Spectrometer (UVCS), among other nine instruments.
Solar flares are the most powerful explosions known in the solar system with an output power equal to a hundred million hydrogen bombs. On November 2003, a solar flare, classified as an X28, was detected at the NOAA´Space Environment Center (SEC), making it the strongest ever recorded. A radio black out occurred just minutes after the eruption of this solar flare which was accompanied by a CME. The strongest solar flares on previous records were classified as X20.
NASA researchers predict the next solar maximum to occur in 2012. During a solar maximum, solar flares are intense; auroras appear in the lower latitudes and radiation disturbs satellite communication. The last solar maximum occurred in the years 2000-2001. The solar minimum, which occurred during 2006, was a period of little solar activity. On January 4, 2008, reversed polarity of the Sun was detected which announces the beginning of the next solar maximum, as well as the start of the next solar cycle.