Photograph by NASA/GSFC/SDO
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NASA's Solar Dynamics Observatory caught this image of an X9.3 solar flare on September 6.

Photograph by NASA/GSFC/SDO

How the Strongest Solar Flare in a Decade Is Affecting Earth

The monster burst of radiation already caused brief radio blackouts and may trigger strong auroras in the coming days.

Early Wednesday morning, the sun unleashed two monster solar flares, the second of which was the most powerful we’ve seen in more than a decade. The burst of radiation was so intense, it caused high-frequency radio blackouts across the daytime side of Earth that lasted for about an hour.

Solar flares are giant explosions on the surface of the sun that occur when twisted magnetic field lines suddenly snap and release massive amounts of energy.

Watch the Sun Blast Out the Biggest Solar Flare in a Decade

The most massive solar flare in over a decade erupted from the sun on September 6, following a smaller, but still intense burst. In addition to a blast of radiation that hit Earth within minutes, a secondary wave of charged particles called a coronal mass ejection affected satellites, GPS, and power grids.

Space weather scientists classify flares based on their intensity, with X-class flares being the most powerful. These explosions can release as much energy as a billion hydrogen bombs.

According to the National Oceanic and Atmospheric Administration's Space Weather Prediction Center, the sun began unleashing its fury on Wednesday at 5:10 a.m. ET, with an X2.2 flare. Just three hours later, the sun produced a second flare measuring a whopping X9.3—the most powerful on record since 2006.

The strongest solar flare measured in modern times happened in 2003, when scientists recorded a blast so powerful that it was off the charts at X28.

On Thursday morning, scientists using the Solar and Heliospheric Observatory, or SOHO, satellite confirmed that an accompanying giant cloud of charged particles, called a coronal mass ejection, now has Earth in its crosshairs. (Find out how sun-watchers stopped World War III in 1967.)

Even a glancing blow to our planet’s magnetic field from a powerful CME can trigger a geomagnetic storm, which can disrupt satellites, GPS navigation, and the power grid but can also spawn especially brilliant auroras. SOHO scientists predict that a strong geomagnetic storm will hit on September 8.

Sky-watchers, particularly those in high-latitude regions, should be on the lookout for auroras visible in the northern skies over the course of this week and into the weekend.

And the sun may not be over its tantrum yet. The same sunspot group that sparked the Wednesday flares, known to scientists as active region 2673, belched out a medium M-class flare on Tuesday that also triggered an aurora alert.

While the sun is now heading toward the minimum level of activity in its natural 11-year cycle, these sunspots could continue to flare up in the days ahead.

Sun 101
Note: This story was updated on September 7.

Andrew Fazekas, the Night Sky Guy, is the author of Star Trek: The Official Guide to Our Universe. Follow him on Twitter, Facebook, and his website.