Pants on! A Promising Aurora Forecast for Sept. 27-29

A stunning aurora blooms in the sky over Alaska in 2014. Skywatchers may see more modest displays of northern lights early Monday morning and Monday night into Tuesday morning. John Chumack

There's a good possibility we'll see the northern lights the next couple nights due to an increase in the strength of the solar wind from two recent coronal holes. A minor G1 storm is expected to kick up between 1 a.m. and 4 a.m. Central Time Monday morning, Sept. 28. While that's not exactly a friendly time to get up at least the bright moon won't spoil the view — it sets between 3 and 3:30. 

A more intense and widespread G2 or moderate storm is forecast to arrive Monday night, Sept. 28 and linger until dawn Tuesday. G1 conditions are expected to start off the evening with activity intensifying to G2 from 10 p.m. to 1 a.m. Central Daylight Time. Auroras typically begin with a low, greenish arc in the northern sky pieced by occasional faint rays. G2 conditions bring multiple arcs along with brighter, taller and more lively rays visible as far south as Colorado, Illinois and Pennsylvania.

This is what a typical moderate (G2) aurora looks like — modest rays and one or more green-hued arcs low in the northern sky. An Iridium satellite made a cameo appearance during the time exposure. Bob King

We haven't had a G2 storm at mid-northern latitudes since August 2019, so I'm pretty excited about this one. That's why I used "pants on" in the title, a description borrowed from the Alberta Aurora Chasers. When someone posts those words on their Facebook page it's time to drop everything, put on your pants and hurry outside to see the aurora.

A wind of electrons and protons — basically stripped apart hydrogen atoms which compose 91 percent of the sun's mass — stream away from the star into interplanetary space. Enhancements in that wind like a massive increase in the number of particles and uptick in their speed can affect Earth's magnetic field. 

Instead of just blowing by like a gentle breeze they can link into the field and be guided along magnetic lines of force into the upper atmosphere at high speed. There the solar particles strike and excite atoms and molecules of oxygen and nitrogen. As the atoms settle back to their previous "relaxed" state, they release tiny bursts of green and red light that together make the aurora. 

The bad boy coronal hole that blasted a stream of subatomic particles in Earth's direction on Sept. 26 is outlined in red. Normally, the sun's magnetic field prevents gases from leaving the sun, but coronal holes are cooler regions in the its corona where material can escape directly into space. Ultraviolet light image by NASA's Solar Dynamics Observatory

Two recent "holes" in the sun's outer atmosphere, known as the corona, have unleashed torrents of high-speed particles our way. The first arrives tonight, and the second tomorrow night. There's just one fly in the ointment. The moon. It's just a few days from full, bright enough nearly erase a G1 storm. I think we'll still see the G2 storm despite moonlight, but it will be compromised.

Your best strategy is to watch during the peak but also to get up before dawn for another go-round after moonset. The moon will set Monday morning between 3-3:30 a.m., leaving a 2-hour viewing "window," and around 4:30 a.m. Tuesday morning with a 1-hour window.

I hate to toss in another caveat, but remember that all auroral forecasts are subject to change. Sometime the aurora arrives earlier or later than expected or fails to show up altogether. I'll update with more information (and a new forecast if any) tonight and again on Monday. You can also check SpaceWeatherLive for updates. Keep your fingers crossed!