Green vs. red, north vs. south: The solar storm that swept over our planet on Wednesday provided the perfect opportunity for a study in auroral contrasts.
When electrically charged particles from a coronal mass ejection, or CME, interact with ions and molecules high up in Earth's atmosphere, waves of light can ripple along magnetic field lines.
Wednesday's outburst was exceptional: Skywatchers as far south as Kansas, Ohio and Oklahoma could catch the show. But the best viewing was available from more northerly (or southerly) latitudes. Finnish photographer Thomas Kast was in the right place at the right time to capture a prize picture.
"For a long time I wanted to capture auroras with a field of sparse tall trees," he said. "The huge layer of faint green in the sky brought out the silhouettes even better than I hoped for. At times it was very foggy, as you can see at the bottom. What an amazing atmosphere it was!"
Half a world away, Minoru Yoneto snapped a picture of a ruddy aurora australis, as seen from Queenstown, New Zealand. "This is how the sky looked 11 hours after the CME impact," Yoneto told SpaceWeather.com.
Auroral lights usually glow in shades of green and sometimes purple. Red is more rare, said SpaceWeather.com's Tony Phillips.
"Red auroras occur some 300 to 500 kilometers above Earth's surface and are not yet fully understood," he wrote. "Some researchers believe the red lights are linked to a large influx of electrons. When low-energy electrons recombine with oxygen ions in the upper atmosphere, red photons are emitted. At present, space weather forecasters cannot predict when this will occur."
There's one thing about auroras that's easy to predict: SpaceWeather.com's gallery can be counted upon to have the latest and greatest pictures of the northern (and southern) lights. Check out the bonus pictures from Swedish photographer Göran Strand, and then follow the links for still more auroral glories.
More auroral glories:
- Northern lights cast an alien glow
- Slideshow: Best of the northern lights
- Photoblog archive of aurora pictures
Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with NBCNews.com's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.