July 16, 2012 Over the July 14-15, 2012 weekend and through the early morning of July 16, Earth experienced what's called a geomagnetic storm, which happens when the magnetic bubble around Earth, the magnetosphere, quickly changes shape and size in response to incoming energy from the sun. In this case that energy came from a coronal mass ejection (CME) associated with a July 12 X-class flare.
Geomagnetic storms can create aurora visible at lower latitudes than usual, and aurora were spotted in the US as far south as Missouri and Arkansas.
Rough estimates based on the data currently available -- namely observations from STEREO-B (the Solar Terrestrial Relations Observatory) -- show that the CME was traveling in an Earth direction at over 850 miles per second.
The X1.4 class flare erupted from the center of the sun, peaking on July 12, 2012 at 12:52 PM EDT. It erupted from Active Region 1520 which rotated into view on July 6.
What is a solar flare? What is a coronal mass ejection?
For answers to these and other space weather questions, visit NASA's Spaceweather Frequently Asked Questions page (http://www.nasa.gov/mission_pages/sunearth/spaceweather/index.html)
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