Solar Flare Classifications

Ranking of a solar flare is based on its x-ray output. Flares are classified according to the order of magnitude of the peak burst intensity (I) measured at the earth in the 0.1 to 0.8 nm wavelength band as follows:
Peak, 0.1 to 0.8 nm band 
Class (Watts/square metre) 
B I < 10-6 
C 10-6 I < 10-5 
M 10-5 I < 10-4 
X I 10-4 
A multiplier is used to indicate the level within each class. For example: 

M6 = 6 X 10-5 Watts/square metre 

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