Picture of the month

This image of the Sun shows a large solar flare (on the right side of the picture) coming from a giant active region called AR2673 just as the region is about to disappear behind the solar horizon. Since 6 September, AR2673 has been responsible for several flares including the largest seen in more than a decade. The large flare shown here, captured in ultraviolet by the Atmospheric Imaging Assembly on the Solar Dynamics Observatory mission, was followed by a large coronal mass ejection (CME) on 10 September. While solar flares are responsible for emission in the ultraviolet and X-ray regions, gamma-rays with an energy of several GeV have been measured in the past by the Fermi-LAT satellite. CMEs. which often follow solar flares, are responsible for the ejection of high-energy electrons and protons into the solar system resulting in the Northern Lights. Although the CMEs coming from this region resulted in spectacular Northern Lights, much stronger CMEs have occurred in the past. In 1859 a CME was strong enough to cause auroras to be visible at latitudes as low as Cuba, while the results of a very strong solar event in the year 775 are thought to be responsible for a large carbon-14 surplus found in tree rings around the world.

About the author

Compiled by Merlin Kole, Department of Particle Physics, University of Geneva.