The sun's been cookin' lately! Sunspots have freckled its disk the past few days, including a group named Active Region 2860. It's more than 43,000 miles (70,000 km) across — larger than five Earths! On the 28th it blew off a significant flare directed squarely at our planet. That could mean additional northern lights opportunities by mid-week.
Sunday, Aug. 29, however, a solar blast from an earlier flare in a different region will blitz the planet. If we're lucky, the material, which carries part of the sun's magnetic field, will find a way to connect with our own magnetic bubble and stoke up a little aurora.
The latest space weather forecast calls for a minor G1 storm between 7 p.m. and 1 a.m. Central Daylight Time. Skywatchers in the northern U.S. and Canada could see a pale green arc low in the northern sky as soon as it gets dark. Based on past experience and trends, most auroras are best between about 11 p.m. and 2 a.m. local daylight time. A display often begins with a faint arc that gradually brightens, so if you plan to watch, find a dark place with a good northern view. Many times, the early signs of the aurora won't be visible except from the country where your eyes can fully adapt to the darkness.
Often, the arc will double. And if things are really going your way, all at once, vertical beams called rays may appear and slowly sweep back and forth above the arc. Time exposures with a camera frequently reveal that ray tops are colored deep-red (hard to see with your eyes), while the brightest parts appear pale green. Both colors are due to excited oxygen atoms high in the ionosphere. Slammed by miniscule solar bullets (electrons) moving at around 45 million miles an hour (72 million km/hour), the atoms release red and green light as they quickly relax back to their original or "ground" state.
If you see deep red at the bottoms of the rays near the horizon, that's from excited nitrogen. Nitrogen higher up also can glow blue or purple during intense displays. Oxygen and nitrogen are the two most common gases in our atmosphere. Think of the aurora as nature's version of a neon sign, but instead of plugging it in to get the current flowing, fast-moving electrons accelerated by electric and magnetic fields do the job.
Despite the energy and speeds involved, watching the northern lights is a hushed affair. A chance to be still and enjoy the night's quietude in a rural place. Some folks claim to hear shushing and crackling noises, but in the hundreds of displays I've witnessed in the past 40 years I've never heard a peep. That doesn't preclude sounds, but when (if) they do happen, they're certainly uncommon.
Besides light, the aurora also generates very low frequency radio waves, and these can be converted into sound with an appropriate VLF (Very Low Frequency) receiver. I own one of these and can tell you that the northern lights can produce amazing and bizarre sounds that resemble a chorus of frogs or birds.
Although the aurora was active Friday night, Aug. 27, we were clouded out here in northern Minnesota. The forecast looks more lights-friendly tonight with no moon until around 11:30 p.m. I'll be facing north with hope in my heart and hope you'll join me.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.