A sudden, intense burst of radiation from the sun's surface, released when magnetic energy built up in the sun's atmosphere is abruptly released, often in the vicinity of sunspots. The largest flares can temporarily disrupt radio communication and GPS signals on the sunlit side of Earth within minutes, and are frequently, though not always, accompanied by a coronal mass ejection that can trigger a geomagnetic storm and enhanced aurora a day or two later.
Facts
PeriodicityVaries with the 11-year solar cycle 1 ScaleClassified A, B, C, M or X by peak soft X-ray flux (0.1 to 0.8 nanometres) 1 First DescribedFirst observed independently by Richard Carrington and Richard Hodgson on 1 September 1859 1 Connections
Associated With
A sufficiently powerful solar flare, especially one paired with a coronal mass ejection, is a direct and well-established trigger of a geomagnetic storm when the ejected material reaches Earth's magnetosphere.
Sources
1. Solar flare, Wikipedia
Occurrence and solar cycle
The occurrence of solar flares varies with the 11-year solar cycle.
Observation history
Solar flares were first observed by Richard Carrington and Richard Hodgson independently on 1 September 1859 by projecting the image of the solar disk produced by an optical telescope through a broad-band filter.
Classification
The modern classification system for solar flares uses the letters A, B, C, M, or X, according to the peak flux in watts per square metre (W/m2) of soft X-rays with wavelengths 0.1 to 0.8 nanometres.
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