flare

A sudden eruption of energy in the solar atmosphere lasting minutes to hours, from which radiation and particles are emitted. Flares are classified on the basis of area at the time of maximum brightness in H-alpha and on the peak flux of 1 minute averaged GOES XRS 0.1 – 0.8 nm band x-rays.  For x-ray flare classifications, see the definition for x-ray flare class.  The H-alpha classifications are given here..
Importance 0 (Subflare):
<= 2.0 hemispheric square degrees
Importance 1:
2.1-5.1 square degrees
Importance 2:
5.2-12.4 square degrees
Importance 3:
12.5-24.7 square degrees
Importance 4:

= 24.8 square degrees
[One square degree is equal to (1.214 x 104 km2) = 48.5 millionths of the visible solar hemisphere.] A brightness qualifier F, N, or B is generally appended to the importance character to indicate faint, normal, or brilliant (for example, 2B).