First X-Class Solar Flares of 2013 – NASA

On May 12-13 the Sun erupted with an X1.7-class and an X2.8-class flare as well as two coronal mass ejections, or CMEs. Solar flares are classified as A, B, C, M or X according to the peak flux.


ClassificationPeak Flux Range at 100-800 picometre
(Watts/square metre)
A< 10−7
B10−7 – 10−6
C10−6 – 10−5
M10−5 – 10−4
X> 10−4


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