Solar storms hit the Earth on a fairly regular basis, but here on terra firma, we can’t really see them when we’re in the middle of them. But now with the STEREO probe way out in space studying the Sun, it was able to turn its eye back onto the Earth to watch our tiny blue dot get completely engulfed in a massive solar storm.
“We have seen CMEs before, but never quite like this,” says Lika Guhathakurta, program scientist for the STEREO mission at NASA headquarters. “STEREO-A has given us a new view of solar storms.” STEREO-A is one of two spacecraft launched in 2006 to observe solar activity from widely-spaced locations. At the time of the storm, STEREO-A was more than 65 million miles from Earth, giving it the “big picture” view other spacecraft in Earth orbit have been missing.
When CMEs first leave the sun, they are bright and easy to see. Visibility is quickly reduced, however, as the clouds expand into the void. By the time a typical CME crosses the orbit of Venus, it is a billion times fainter than the surface of the full Moon, and more than a thousand times fainter than the Milky Way. CMEs that reach Earth are almost as gossamer as vacuum itself and correspondingly transparent.
“Pulling these faint clouds out of the confusion of starlight and interplanetary dust has been an enormous challenge,” says DeForest. Indeed, it took almost three years for his team to learn how to do it. Footage of the storm released today was recorded back in December 2008, and they have been working on it ever since. Now that the technique has been perfected, it can be applied on a regular basis without such a long delay.
Alysha Reinard of NOAA’s Space Weather Prediction Center explains the benefits for space weather forecasting:“Until quite recently, spacecraft could see CMEs only when they were still quite close to the sun. By calculating a CME’s speed during this brief period, we were able to estimate when it would reach Earth. After the first few hours, however, the CME would leave this field of view and after that we were ‘in the dark’ about its progress.”
“The ability to track a cloud continuously from the Sun to Earth is a big improvement,” she continues. “In the past, our very best predictions of CME arrival times had uncertainties of plus or minus 4 hours,” she continues. “The kind of movies we’ve seen today could significantly reduce the error bars.”