Two powerful 'X-class' flares erupt on sun (+video)

Astronomers rank solar flares by strength using five categories: A, B, C, M and X. The A-class flares are the weakest sun storms, while the X-class events are the most powerful solar flares.

This ranking system was designed by the National Oceanic and Atmospheric Administration and resembles the Richter scale used for earthquakes in that each category is 10 times stronger than the one before it, NASA officials have said. So a B-class solar flare is 10 times stronger than an A-class event, while a C-class solar storm releases 10 times more energy than B-class flare (or 100 times more energy than an A-class event).

The categories are also broken down into subsets, from 1 to 9, to pinpoint a solar flare's strength. Only X-class solar flares have subcategories that go higher than 9. The most powerful solar flare on record occurred in 2003 and was estimated to be an X28 on the solar flare scale, NASA officials said. 

Tuesday's X-class solar flares followed a string of other eruptions that included M-class and C-class events, space weather officials said. Both of the day's X-class sun storms were stronger than the X1.1 solar flare of March 5.

Prior to this week, the only huge solar flare of 2012 occurred on Jan. 27, when the sun unleashed an X1.7-class eruption.

The sun is currently going through an active phase of its 11-year weather cycle. The current cycle is known as Solar Cycle 24 and is expected to reach its peak level of activity in 2013, NASA officials have said.

You can follow SPACE.com Managing Editor Tariq Malik on Twitter @tariqjmalik. Follow SPACE.com for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.

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