The events leading to the colorful display began Saturday, when a solar flare erupted. The flare was not particularly large, but it was positioned centrally on the Earth-facing side of the solar sphere. More critically, a coronal mass ejection (CME) also accompanied the flare.
CMEs, although less spectacular than the flash of a flare, are the element that send Earth’s magnetic field into a frenzy. They add enormous amounts of energy to the near-Earth environment and help spawn the otherworldly colors, which are excited nitrogen and oxygen molecules releasing photons of light. Strong geomagnetic storms may sometimes affect electrical power grids, GPS positioning and various types of communications.
Think of a CME’s transit the way a batter sees a pitch coming from the pitcher’s mound. Speed is important, clearly, but more than that, the spin on the baseball dictates where the pitch will end up and how effective it will be. Though CMEs don’t spin, they do carry a magnetic field component; but the magnitude is unknown until the CME travels within 1 million miles of Earth, where spacecraft can measure it.
Geomagnetic activity increased as this CME approached Earth, spurring minor to moderate storm (G1-G2) storm conditions. Some ground reports even hint at another dancing light display that sometimes accompanies auroras called STEVE (short for Strong Thermal Emission Velocity Enhancement), although researchers are still verifying the reports.
“Citizen scientists reported some unusual arcs on the southern edge of the auroral activity. Definitely a classic STEVE but also something looked more anomalous in structure and color,” Liz MacDonald, a space scientist at NASA, wrote to us.
If you saw an aurora or STEVE, report your observations to the citizen-science project Aurorasaurus to help researchers improve aurora forecasting and learn more about STEVE.
There’s a chance for lingering auroral shows Tuesday night. But also, over the next few years be mindful of the sun making a splash, with more space weather storms in the offing.
Until then, enjoy these beautiful aurora photographs captured by dedicated sky watchers. Reports range from Alberta to Nebraska to Maine to space.
U.S. West Coast
U.S. East Coast
Kasha Patel contributed to this report.