The Most Powerful Solar Flares Ever Recorded

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Ranking Day/Month/Year X-Ray Class
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  1             04/11/03              X28+
  2             02/04/01              X20.0
  2             16/08/89              X20.0
  3             28/10/03              X17.2
  4             07/09/05              X17
  5             06/03/89              X15.0
  5             11/07/78              X15.0
  6             15/04/01              X14.4
  7             24/04/84              X13.0
  7             19/10/89              X13.0
  8             15/12/82              X12.9
  9             06/06/82              X12.0
  9             01/06/91              X12.0
  9             04/06/91              X12.0
  9             06/06/91              X12.0
  9             11/06/91              X12.0
  9             15/06/91              X12.0
  10            17/12/82              X10.1
  10            20/05/84              X10.1
  11            29/10/03              X10
  11            25/01/91              X10.0
  11            09/06/91              X10.0
  12            09/07/82              X 9.8
  12            29/09/89              X 9.8
  13            22/03/91              X 9.4
  13            06/11/97              X 9.4
  14            24/05/90              X 9.3
  15            05/12/06              X 9.0  
  15            06/11/80              X 9.0 
  15            02/11/92              X 9.0
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This list is based in part on "Large Solar Flares Since 1976" compiled by IPS Radio & Space Services. The two most recent entries (Dec. 5, 2006; Sept. 7, 2005) are highlighted in red.

The Classification of X-ray Solar Flares

02/04/01 X20.0

A solar flare is an explosion on the Sun that happens when energy stored in twisted magnetic fields (usually above sunspots) is suddenly released. Flares produce a burst of radiation across the electromagnetic spectrum, from radio waves to x-rays and gamma-rays.

Scientists classify solar flares according to their x-ray brightness in the wavelength range 1 to 8 Angstroms. There are 3 categories: X-class flares are big; they are major events that can trigger planet-wide radio blackouts and long-lasting radiation storms. M-class flares are medium-sized; they can cause 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.

Each category for x-ray flares has nine subdivisions ranging from, e.g., C1 to C9, M1 to M9, and X1 to X9. In this figure, the three indicated flares registered (from left to right) X2, M5, and X6.

Class	Peak (W/m²)between 1 and 8 Angstroms
B	I < 10^-6
C	10^-6 < = I < 10^-5
M	10^-5 < = I < 10^-4
X	I > = 10^-4

The Sun

Credit: NASA, SOHO, JPL , LASCO