NOAA forecasters have upgraded the chance of X-class solar flares today (November 4, 2011) to 20%. The source would be one of the largest sunspots in years that has just rotated into view, over the sun’s northeastern visible edge. Designated AR1339, it is some 25,000 miles (40,000 kilometers) wide and at least twice that in length. That means you could line six planet Earths up side by side in front of AR1339’s long dimension.
Sunspot AR1339 already spawned an X1.9-class solar flare on November 3, 2011 at around 20:27 UTC (3:27 p.m. CDT). An X-class flare is the most powerful of the solar flare categories defined by NASA. The coronal mass ejection (CME) from yesterday’s X-class flare is not headed toward Earth, but it will strike Mercury and Venus.
NASA Goddard’s Space Weather Lab is tracking the CME from yesterday’s X-class solar flare. The cloud of plasma ejected off the sun at 1,100 kilometers/second (680 miles/second). It should hit Mercury midday today according to U.S. clocks. NASA’s MESSENGER probe around Mercury will be monitoring the impact. The CME will hit Venus sometime tomorrow.
This CME will not strike Earth, as you can see by looking carefully at the “prediction track” below:
Sunspots appear visibly dark in contrast to the brilliant solar surface surrounding them, but if you could remove them from the sun’s surface they would appear to shine brightly. They are caused by intense magnetic activity on the sun, and, like magnets, sunspots also have a north and south magnetic pole. Sunspots are highly variable. They come and go, expand and contract, appear on the sun’s surface and then disappear. And of course they are subject to the famous, approximate 11-year cycle of solar activity. We’re near the peak of that cycle at this time, which is why we’ve posted many article recently about sunspots and X-flares!
By the way, here’s a cool movie of the November 3, 2011 X-flare from AR1339.
Bottom line: One of the largest sunspots in years rotated into view over the past few days, over the sun’s northeastern visible edge. Designated AR1339, it is some 25,000 miles (40,000 kilometers) wide and at least twice that in length. It spawned an an X1.9-class solar flare on November 3, 2011. NOAA forecasters have upgraded the chance of X-class solar flares today (November 4, 2011) to 20%.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.