I sure wish I’d been up at 3 o’clock this morning. That’s when a surprise aurora hit. In a very short time, conditions went from a minor G1 storm to a strong G3. For several hours until around 6:30 a.m. CDT, the storm would have been visible (before twilight grew too bright) across the northern third of the U.S. Things have quieted down now, but more is on the way.
Multiple coronal mass ejections (CMEs) from the region around sunspot group 2741 on May 10, 12 and 13 are headed in Earth’s direction as you read this. The pileup should arrive over the next two days — May 15 and 16 — and produce minor to moderate (G1-G2) geomagnetic storms. CMEs are clouds of protons and electrons shot into space at over a million miles an hour. A solar flare can launch a CME. So can instabilities in magnetic fields surrounding sunspots.
On May 12 over a period of hours, a dark filament of incandescent hydrogen gas erupted and left the sun headed in our direction. Filaments are just prominences — those fiery pink “flames” we see around the edge of the sun during a total solar eclipse — seen in silhouette against the bright solar surface. A filament looks like an eyelash when viewed through a specialized filter. Filaments “body surf” atop invisible magnetic fields. When those fields become unstable, they can launch the filament into space.
The sun connives to rattle the Earth and its inhabitants in many ways, so keep your eyes peeled for northern lights the next few nights. There’s just one caveat — the moon. It’s getting bigger and brighter with each passing night. Its light not only washes out fainter auroras but illuminates the thicker, denser air near the horizon, mimicking the glow of a low auroral display.
A display usually starts as a low arc or glow about a fist or 10° above the northern horizon. You’ll know if you’re seeing aurora by shape and movement. Auroras come in arcs and vertical streaks, not the formless “blooms” of city light pollution that blot our horizons nowadays. FYI, horizontal streaks are almost always clouds. Watch for movement. If you see a glowing patch disappear and then reappear in the same area, that’s the aurora. If a patch slowly drifts in one direction, it’s a cloud.
You can always get the latest 3-day spaceweather forecast here, which describes activity every 3 hours by a Kp number from 0 to 9. A “5” is a minor storm; a “6” a moderate one and a “7” a strong storm. Also, be sure to check the extent of the aurora to see if it’s spreading southward in your direction at the 30-minute forecast site. This site shows the extent of the northern and southern auroral ovals, permanent rings of aurora centered on Earth’s geomagnetic poles.
Clear skies would be nice. Let’s hope we get them.