STEREO
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STEREO is a solar observation mission. Two nearly identical spacecraft were launched in 2006 into orbits around the Sun that cause them to respectively pull farther ahead of and fall gradually behind the Earth. This enabled stereoscopic imaging of the Sun and solar phenomena, such as coronal mass ejections.
Illustration of a STEREO spacecraft during solar array deployment
STEREO spacecraft in Delta II fairing
STEREO probes stacked at Astrotech in Florida August 11, 2006
Launch of the STEREO probes on a Delta II rocket October 26, 2006
Coronal mass ejection
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A coronal mass ejection (CME) is a significant ejection of magnetic field and accompanying plasma mass from the Sun's corona into the heliosphere. CMEs are often associated with solar flares and other forms of solar activity, but a broadly accepted theoretical understanding of these relationships has not been established.
Photo from the ISS of aurora australis during a geomagnetic storm on 29 May 2010. The storm was most likely caused by a CME that had erupted from the Sun on 24 May 2010, five days prior to the storm.