CME Week: Mapping the Journey of a Giant Coronal Mass Ejection

Two main types of explosions occur on the sun: solar flares and coronal mass ejections. Unlike the energy and X-rays produced in a solar flare – which can reach Earth at the speed of light in eight minutes – coronal mass ejections are giant clouds of solar material that take one to three days to reach Earth. Once at Earth, these ejections, also called CMEs, can impact satellites in space or interfere with radio communications. During CME Week from Sept. 22 to 26, 2014, we explore different aspects of these giant eruptions that surge out from our closest star.

On July 23, 2012, a massive cloud of solar material erupted off the sun’s right side, zooming out into space. It soon passed one of NASA’s Solar Terrestrial Relations Observatory, or STEREO, spacecraft, which clocked the CME as traveling between 1,800 and 2,200 miles per second as it left the sun. This was the fastest CME ever observed by STEREO.

Two other observatories – NASA’s Solar Dynamics Observatory and the joint European Space Agency/NASA Solar and Heliospheric Observatory — witnessed the eruption as well. The July 2012 CME didn’t move toward Earth, but watching an unusually strong CME like this gives scientists an opportunity to observe how these events originate and travel through space.

STEREO’s unique viewpoint from the sides of the sun combined with the other two observatories watching from closer to Earth. Together they helped scientists create models of the entire July 2012 event. They learned that an earlier, smaller CME helped clear the path for the larger event, thus contributing to its unusual speed.

Such data helps advance our understanding of what causes CMEs and improves modeling of similar CMEs that could be Earth-directed.

Watch the movie to see how NASA’s solar-observing missions worked together to track this CME.

**Karen C. Fox
NASA’s Goddard Space Flight Center, Greenbelt, Md.**

Related Links

• More on CME Week
• More on the July 23, 2012 CME

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