NASA / LMSAL via SpaceWeather. com
This color-coded image combines observations made by NASA's Solar Dynamics Observatory in several extreme ultraviolet wavelengths, highlighting a bright X-class flare toward the upper left of the sun's disk on March 6.
The sun unleashed one of the biggest flares ever seen during its current activity cycle late Tuesday — an X5.4-class outburst strong enough to trigger a radio blackout. The resulting geomagnetic storm could affect electrical grids, communication links, satellite navigation systems and airline schedules over the next couple of days.
The outburst at 7:24 p.m. ET was followed about an hour later by an X1.3-class blast. Solar flares are rated on a letter-plus-number scale, with X being the most powerful category. Usually the numbers run from 1 to 9, but X-class flares can run higher. The highest reading recorded recently is an X28, observed in 2003.
Joe Kunches, a space scientist with the National Oceanic and Atmospheric Administration's Space Weather Prediction Center, says the double blast made for a "Super Tuesday," in a different sense from the political meaning.
The big question is, what effect will this solar activity have on Earth? The solar blasts threw off waves of electrically charged particles known as coronal mass ejections, or CMEs. Those waves are now speeding outward, and space-weather forecasters expect them to touch off strong geomagnetic storms when they interact with Earth's magnetic field late Wednesday and early Thursday.
"The most northern states in the 'Lower 48' should have a chance to see the aurora," the prediction center reported on Facebook.
Could something more serious happen? All this activity is already whipping up an S3 solar radiation storm. "Such a storm is mainly a nuisance to satellites, causing occasional reboots of onboard computers and adding noise to imaging systems," SpaceWeather.com's Tony Phillips said.
The coming geomagnetic storm is predicted to reach the G3 level, which could trigger alarms on electrical power systems and create intermittent problems for GPS navigation services. Some airline flights are likely to be rerouted so they don't fly so close to the poles, and problems could arise with communication systems in polar regions. That's the bad news. The good news is that NASA and NOAA have lots of resources in space to monitor solar activity, giving network operators more time to assess and prepare.
Check out NOAA's chart of space weather scales to learn more about what S3, G3 and the other storm desigations mean.
Experts at the Space Weather Prediction Center say the storm generated by the X5.4-class flare is on a trajectory to deliver a glancing blow rather than a direct hit on Earth, but they caution that the sunspot region responsible for the flare, AR1429, "remains potent, and subsequent activity is certainly possible."
For now, chances are that the most noticeable effect for most people will be an upswing in the number of fantastic pictures of the northern lights. AR1429 has been acting up over the past few days, and SpaceWeather.com has been adding plenty of stunners to its aurora gallery. If you get a nice snapshot, please consider sharing it with us via the Cosmic Log Facebook page or msnbc.com's FirstPerson in-box.
The solar storm could cause communication problems, affecting radio and satellite systems. NBC's Tom Costello reports.
Update for 4:40 p.m. ET March 7: NASA's Goddard Space Flight Center reports that the coronal mass ejections sent out on Tuesday are projected to impact Earth and Mars as well as several interplanetary spacecraft, including NASA's Spitzer Space Telescope, the Messenger probe at Mercury and the sun-watching STEREO-B satellite. The NASA advisory also notes that the X5.4-class flare was the strongest solar outburst since an X6.9 blast on Aug. 9, 2011. In that previous case, the resulting CME was not directed at Earth, and no ill effects were felt.
Update for 5 p.m. ET March 7: A lot of commenters are talking about the Carrington Event of 1859, a solar storm that was so strong it frazzled telegraph wires. That was associated with what was surely an off-the-scale solar flare, much more powerful than the X28 referenced at the beginning of this item — so I've rephrased that reference accordingly.
More about solar storms and auroras:
- Northern lights shine through a crack
- Rocket flies into the northern lights
- Aurora extravaganza glows in space
- Planet looks back at the northern lights
- Slideshow: The best of the northern lights
- Cosmic Log's auroral archive
This item was first published at 12:30 a.m. ET March 7.
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.