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This image provided by NASA shows a solar flare early Tuesday, Aug. 9, 2011, the largest in 5 years. The image was was captured by NASA's Solar Dynamics Observatory (SDO) in extreme ultraviolet light at 131 Angstroms. Scientists say the bursts of radiation hurled by the solar blast were not in the direction of Earth, so there’ll be little impact to satellites and communication systems. (AP Photo/NASA)

LOS ANGELES (AP) — The sun unleashed a powerful solar flare early Tuesday, the largest in nearly five years.

Scientists say the eruption took place on the side of the sun that was not facing Earth, so there'll be little impact to satellites and communication systems.

The flare had a GOES X-ray magnitude of X6.9, meaning it was more than 3 times larger than the previous largest flare of this solar cycle: the X2.2 that occurred on Feb 15, 2011. Space scientist Joe Kunches at the government's Space Weather Prediction Center in Colorado says there were reports of brief short-wave radio disruptions in Asia, but little else.

The sun is transitioning from a quiet period into a busier cycle. Scientists estimate there will be a spike in the number of such solar eruptions over the next three to five years.

The last time there was such a strong solar flare was in December 2006.

What signifies an X-class flare?

Solar flares are giant explosions on the sun that send energy, light and high speed particles into space. These flares are often associated with solar magnetic storms known as coronal mass ejections (CMEs). The number of solar flares increases approximately every 11 years, and the sun is currently moving towards another solar maximum, likely in 2013. That means more flares will be coming, some small and some big enough to send their radiation all the way to Earth.

The biggest flares are known as "X-class flares" based on a classification system that divides solar flares according to their strength. The smallest ones are A-class (near background levels), followed by B, C, M and X. Similar to the Richter scale for earthquakes, each letter represents a 10-fold increase in energy output. So an X is ten times an M and 100 times a C. Within each letter class there is a finer scale from 1 to 9.

C-class and smaller flares are too weak to noticeably affect Earth. M-class flares can cause brief radio blackouts at the poles and minor radiation storms that might endanger astronauts.

And then come the X-class flares. Although X is the last letter, there are flares more than 10 times the power of an X1, so X-class flares can go higher than 9. The most powerful flare measured with modern methods was in 2003, during the last solar maximum, and it was so powerful that it overloaded the sensors measuring it. The sensors cut out at X28.

The biggest X-class flares are by far the largest explosions in the solar system and are awesome to watch. Loops tens of times the size of Earth leap up off the sun's surface when the sun's magnetic fields cross over each other and reconnect. In the biggest events, this reconnection process can produce as much energy as a billion hydrogen bombs.

If they're directed at Earth, such flares and associated CMEs can create long lasting radiation storms that can harm satellites, communications systems, and even ground-based technologies and power grids. X-class flares on December 5 and December 6, 2006, for example, triggered a CME that interfered with GPS signals being sent to ground-based receivers.

NASA and NOAA?as well as the US Air Force Weather Agency (AFWA) and others?keep a constant watch on the sun to monitor for X-class flares and their associated magnetic storms. With advance warning many satellites and spacecraft can be protected from the worst effects.

Recent solar events

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