Sun erupts with the summer's strongest solar flare

The most powerful solar flare of the summer erupted from the sun on Friday, marking the latest in a string of strong storms this week from our home star.

The sun storm occurred just after 7 p.m. ET and registered as a class X1.1 solar flare — one of the strongest types of solar flares possible, according to the U.S. Space Weather Prediction Center, run by NOAA and the National Weather Service.

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The huge solar flare erupted from the giant sunspot AR1515, which has already fired off several other powerful storms this week. Space weather scientists were closely watching the sunspot for possible X-class flares.

"And AR1515 did it! X1-class solar flare," officials with NASA's sun-watching Solar Dynamics Observatory wrote in a post to @Camilla_SDO, the mission mascot's Twitter account.

By all accounts, the sunspot group AR1515 is enormous. It stretches across 118,681 miles (191,000 kilometers) of the sun's surface, making it longer than 15 Earths set end to end, NASA solar astrophysicist C. Alex Young told Space.com before the X1.1-class flare erupted. [More Solar Flare Photos from Sunspot AR1515]

While Friday's solar flare marked the strongest of the summer season, which began in late June, it is not the strongest of 2012. In March, the sun fired off an intense X5.4-class solar flare. Today's sun storm marked the fifth X-class solar flare of the year.

The active sun
Earlier Friday, space weather officials warned of more potential flare-ups from sunspot AR1515. The sun has been undergoing substantial activity this entire week from several sunspots on its Earth-facing side.

"The bulk of activity is coming from Region 1515, a moderate-sized active region with a magnetic field complexity that harbors an isolated chance of X-class flare activity," SWPC officials said in an alert released before the X1.1-class flare.

In a new alert announcing the X-class solar flare, SWPC officials said the sun storm could a "wide-area blackout" in the high-frequency radio communications.

Scientists measure the strength of solar flares in terms of energy classes, with X-class flares being the strongest sun storms. Moderate flares rank as class-M storms and can supercharge Earth's auroral displays when aimed at our planet. Class C-solar flares round out the top three categories, but they have little impact on Earth.

Young said there was a chance the sunspot could trigger a massive explosion of solar plasma known as a coronal mass ejection, or CME.

"The region is still in a position to produce an Earth-directed coronal mass ejection but since it is no longer at disk center the chances are less," Young said. "It should also be noted that even at disk center, CMEs don't always head to Earth."

CMEs unleashed from the sun earlier this week were expected to arrive at Earth in the next two days, possibly amping up geomagnetic activity, SWPC officials said.

Solar flare basics
When aimed directly at Earth, X-class solar flares and CMEs can potentially endanger satellites and astronauts in orbit, interfere with GPS and communications signals, and damage power system infrastructure on the ground.

The sun is currently in the midst of an active phase of its 11-year solar weather cycle. The current cycle is called Solar Cycle 24 and is expected to peak in 2013.

Sunspot group AR1515 is by no means the only active region on the sun.

"There is a new active region that is starting to come into view on the lower half of the sun," Young said. "It should be completely on the Earth-facing side of the solar disk in the next day."

If you snap a photo of sunspot AR1515 or any amazing northern lights photos this week and you'd like to share them for a possible story or image gallery, please send images and comments to managing editor Tariq Malik at tmalik@space.com.

You can follow Space.com Managing Editor Tariq Malik on Twitter@tariqjmalik. Follow Space.com on Twitter @Spacedotcom. We're also on Facebook and Google+.

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