STEREO-A took the photos by using the H1 camera and other instruments in the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) package. The H1 camera looks for solar outflows such as coronal mass ejections, when the sun ejects plasma from its surface into space. Other cameras in the package can look much closer at the sun, either by blocking its light with a coronograph, or by imaging the sun itself in the extreme ultraviolet wavelength, Battams said.
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STEREO-A and a twin spacecraft, STEREO-B, both launched Oct. 25, 2006. They were inserted into sun-centered orbits that trail slightly ahead of and behind the Earth. (The "A" in STEREO-A stands for "Ahead" and the "B" in STEREO-B as stands for "Behind.") With the two spacecraft taking images of the sun at the same time, NASA and the NRL were able to receive stereo data on CMEs and other solar activity.
In October 2014, however, Earth lost contact with STEREO-B. At the time, controllers were resetting and testing the craft to see how well its automation would work when it was behind the sun and in poor contact with Earth. Communication has not been regained.
More images from SECCHI are available online here (click on the thumbnails on the left).
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