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Solar wind puts on light show
The last week saw a series of auroras lighting up the sky in the northern hemisphere.
On the night of 8 October 2015, a photographer in Harstad, Norway captured this image of the dancing northern lights.
Auroras are created when fast-moving, magnetic solar material strikes Earth’s magnetic bubble, the magnetosphere. This collision rattles the magnetosphere in an event called a geomagnetic storm, sending trapped charged particles zooming down magnetic field lines towards the atmosphere, where they collide brilliantly with molecules in the air, creating auroras.
Though many geomagnetic storms are associated with clouds of solar material that explode from the sun in an event called a coronal mass ejection, or CME, this storm was caused by an especially fast stream of solar wind.
“Geomagnetic storms caused by high-speed solar wind streams aren’t uncommon,” says Leila Mays, a space physicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Near solar minimum – when solar activity like CMEs are less frequent – these fast streams are actually the most common cause of geomagnetic storms that create auroras.”
Pictured: The dark area across the top of the sun in this image is a coronal hole, a region on the sun where the magnetic field is open to interplanetary space, sending coronal material speeding out in what is called a high-speed solar wind stream. The high-speed solar wind originating from this coronal hole, imaged by NASA’s Solar Dynamics Observatory, created a geomagnetic storm near Earth that resulted in several nights of auroras. This image was taken in wavelengths of 193 Angstroms, which is invisible to our eyes and is typically colorized in bronze.
Image credit: NASA/SDO
Text credit: Sarah Frazier, NASA’s Goddard Space Flight Center