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Solar activity is classified as A, B, C, D, M or X according to the brightness of its X-rayIn the NATO phonetic alphabet, X-ray represents the letter X. Rontgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz to 60 EHz). X-rays near Earth, measured in W/m\uffff. Each class is ten times more powerful than the preceding one, with X at 10-4 W/m\uffff. Within a class there is a linear scale from 1 to 9, so an X2 flare (twice as powerful as an X1 flare) is four times more powerful than an M5 flare (five times as powerful as an M1 flare). Solar activity is normally within the A to C range. Class D flares have little effect on Earth, while the more powerful M and X flares can cause disruption and damage. Flares generally stay below X10, but infrequently X designations run 'off the charts'. X20 events that were recorded on August 16August 16 is the 228th day of the year (229th in leap years) in the Gregorian Calendar. There are 137 days remaining. Events 1777 American Revolutionary War: Battle of Bennington British forces are defeated by American troops. 1780 American Revolutionary, 19891989 is a common year starting on Sunday (click on link for calendar). Events January January 7 Akihito becomes Emperor of Japan following the death of Hirohito. The Heisei period begins January 8 the Kegworth Air Disaster A British Midland Boeing 737 cra and April 2April 2 is the 92nd day of the year (93rd in leap years) in the Gregorian calendar, with 273 days remaining. Events 1513 Juan Ponce de Leon sets foot on Florida becoming the first known European to do so. 1755 Commodore William James captures pirate fortr, 20012001 is a common year starting on Monday (see link for calendar), and also: The International Year of the Volunteer The United Nations Year of Dialogue Among Civilizations Events January January 1 A black monolith measuring approximately nine feet tall ap were outshone by a flare on November 4November 4 is the 308th day of the year (309th in leap years) in the Gregorian Calendar, with 57 days remaining. Events 1576 Eighty Years' War: In Belgium, Spain captures Antwerp (after three days the city was nearly destroyed). 1612 Moscow China Town tak, 2003 that was the most powerful flare ever recorded in the history of astronomy: an X28. Sunspot Region 486 (shown in the illustration) was the most turbulently active sunspot ever recorded.
Energetic particles emitted by solar flares are a primary contributor to the aurora borealis and aurora australis. See also Solar proton event.
The radiation risk posed by solar flares is one of the major concerns in discussions of manned missions to Mars. Some kind of physical or magnetic shielding will be required.
See also: Coronal mass ejection