Auroras May Dance Over the U.S. Thursday Night, June 4-5

Stormy times may be ahead! NOAA's Space Weather Prediction Center expects a strong (G3 level) geomagnetic storm to arrive the night of Thursday, June 4th, continuing through Friday morning. Should the forecast hold, skywatchers as far south as the central U.S. may witness a fine display of the northern lights. Observers in the northern U.S. might see an exceptional show, with lights reaching as high as the zenith. Keep in mind there's always a chance the storm will arrive late or not reach the expected intensity. Auroras are fickle that way.

The source of the potential storm is the magnetically complex sunspot group dubbed Active Region 4455. Several powerful M-class and one X-class flares erupted within the group over the past few days. Each blasted a coronal mass ejection (CME) in Earth's direction. CMEs are massive clouds of solar particles bundled with the Sun's magnetic field; they move through space at more than 250 kilometers per second, or 560,000 mph.

Under the right circumstances, the CME's magnetic field can couple with Earth's magnetic field, transferring the energy and particles of its magnetosphere into our own. Guided by our planet's magnetic field lines, electrons are accelerated to nearly a tenth the speed of light, raining down onto the nightside polar atmosphere, where they strike and energize nitrogen and oxygen atoms. As they return to the normal or "rest" state, the atoms release tiny bursts of red, green, blue and purple light that together create the shimmering lights that captivate us.

It turns out that one of those recent CMEs moved so swiftly it caught up and "devoured" its slower siblings, creating a cannibal CME. These monsters are even more powerful and known to produce long-lasting storms. That's why the forecast looks good (and why I'm feeling optimistic).

Sunsets are late this time of year and twilights lengthy, too. For most of us that means having to wait until after 10 p.m. local time for the sky to get dark enough to see the aurora. Find a location with as dark a sky as possible in the north direction and try to be patient. Bring a chair, a snack, and a friend. You might not see much at first. But keep your eyes open for a green-hued arc low in the north. If the arc brightens or subdivides into narrow, parallel pillars of light, stick around! Any sign of extra brightening or increasing activity means things are headed in the right direction.

Auroras are typically most active and highest in the sky between about 11 p.m. and 2 a.m. local time. The exact arrival time of the blast is unknown, but your best best is to plan for a late night. Fortunately, the Moon is in waning gibbous phase right now and won't rise until around 12:30 a.m. That means we'll have a nice chunk of dark-sky viewing before moonlight interferes.

To stay abreast of the aurora's whereabouts, please stop by my Facebook page Astro Bob's Astronomy for Everyone. I'll post updates. Another excellent resource is the Michigan Aurora Chasers (also on Facebook). There are also many aurora apps. My favorite is the Glendale app. Not only does it post alerts and lots of great minute-to-minute information about current storms, but aurora-watchers can report and upload their photos to the site. Another good app is Spaceweatherlive. You can see the extent of the auroral ovals — where the aurora is currently active — at NOAA's 30-Minute-Forecast. Now that you're in the know, we just have to wait for the aurora to show. Good luck!