NASA Solar Dynamics Observatory (Little SDO)

In the early hours of October 20, 2011 a M1-class solar flare occurred on the 

side of the Sun and was not Earth directed. This view from the NASA Solar 

Dynamics Observatory shows the event in various wavelengths, which 

corresponds to different temperatures and layers.

It starts at the ~50,000 degrees C. chromosphere (red) and takes us to the 

1 million degree transition region between the chromosphere and the corona

 (yellow) and takes us to the ~2.5 million degrees corona (blue). 

The last segment is a composite of three different wavelengths.

There are three categories of flares, X-class, M-class and C-class. The largest,

 X-class flares are major events that can trigger planet-wide radio blackouts 

and long-lasting radiation storms. M-class flares are medium-sized, capable of

 causing brief radio blackouts that affect Earth's polar regions.

 Minor radiation

 storms sometimes follow an M-class flare. 

Compared to X- and M-class events, 

C-class flares are small with few noticeable consequences here on Earth.