A coronal mass ejection (CME) is a giant cloud of plasma that is projected into interplanetary space. It is one of the most important factors in shaping space weather. On September 24, a professional photographer from Arizona captured one such CME – Andrew McCarthy.
The beautiful and dangerous CME
The CME in question was part of a small G1-class solar storm, the weakest in the NOAA category. It was not facing Earth, so the CME did not cause the aurora borealis in our sky. But, like McCarthy himself admit“It was the greatest CME I’ve ever seen.”
In the attached image, the surface of the Sun and CME are shown in orange, although they are not actually orange. The chromosphere (the lowest region of the Sun’s atmosphere) and CME naturally emit a type of radiation that appears to us as pink and red – this is called hydrogen alpha light (H-alpha).
The frame McCarthy posted is actually a time-lapse photo made up of hundreds of thousands of photos taken in a span of six hours. The final file weighs about 800 GB. Because the exposure time of each image was so short, the original images were almost entirely white. McCarthy digitally added orange when composing the final image to provide contrast between different structures on the Sun’s surface and to emphasize the CME. The rest of the image was not filtered, so the sun retained a stunning white halo that stood out from the dark universe.
CMEs have become more common in recent months as the sun has entered a period of increased solar activity known as the sun’s maximum, which lasts about seven years. This will provide many opportunities for people to take similar photos.
McCarthy warned people not to try to watch the sun without the proper equipment:
Do not point the telescope at the sun. You’ll fry your camera or worse, your eyes. My telescope was specially modified and had several filters that allowed me to take this picture. It cannot be done without preparation.
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