Second Chance: Solar Flare Might Spark Aurora Friday and Saturday Night

Want more? Check out our aurora page, our "How to See the Aurora" video, and Bob King's new book, Magnificent Aurora. 

(Post updated on Oct. 3 at 7:30 p.m. EDT to reflect the revised space weather forecast issued at 6 p.m. EDT).

The Sun unleashed a giant X7.1 flare on October 1st — the second-largest of the current cycle of solar activity, which is now at its maximum. That flare is now forecast to have picturesque repercussions here at Earth on both Friday and Saturday nights, October 4th and 5th. Accompanying the flare was a gale of subatomic particles, now expected to arrive at Earth on Friday morning (Oct. 4th) around 8 a.m. EDT, when it should spark a strong geomagnetic storm — and therefore aurorae.

Unfortunately, only the far northwestern part of the country (Washington state, Alaska) will have dark skies at that time. The revised National Oceanic and Atmospheric Administration forecast predicts moderate G2 storms to occur on both Friday and Saturday nights, Oct. 4th and 5th, starting at nightfall and persisting till dawn. From 2-5 a.m. EDT Saturday, the storm will briefly crest at the G3 level.

Geomagnetic storms occur when the magnetic field embedded in the incoming solar plasma — comprised of electrons and protons — couples with Earth's magnetic field, which guides the material toward the polar regions. Electrons are principally responsible for visible aurorae. They strike and excite oxygen and nitrogen atoms and molecules in the upper atmosphere, and those molecules release their energy as photons of green, red, and purple light when they settle back to their rest states.

To reach the nearly 100 million kilometer per hour (60 million mph) speed needed to excite atmospheric gases, electrons ride "waves in the magnetic field just like a surfer does from ocean waves," according to Cynthia Cattell (University of Minnesota). "The other is from sliding down an electric potential, like a kid sledding down an icy hill."

Solar storms are rated from G1 (minor) to G5 (extreme) depending on how deeply they impact both Earth's protective magnetic shield, called the magnetosphere, and their effects on orbiting satellites and power grids. The impact on our hearts and soul can be profound. A powerful auroral display can move one to tears as surely as watching a total solar eclipse.

Should the Space Weather Prediction Center (SWPC) forecast pan out, observers in the northern states should see the aurora Friday night as soon as dusk. Later that night, it could easily reach the zenith and possibly spill over into the southern sky. Farther south, in Illinois, Iowa, and Oregon, skywatchers might see arcs and rays in the lower third of the northern sky. Even observers in the south-central U.S. may see a modest glow at the horizon and record red-hued aurorae in time-exposures.

How lucky we are that the Moon is just a thin crescent and won't disrupt the view. The aurora is usually best later at night around midnight to 1 a.m. local time, because the auroral ovals — the bagel-shaped regions centered on the north and south geomagnetic poles where the incoming solar particles strike the atmosphere — expand furthest south toward the northern U.S. at that time.

To see this event best, find a location with a dark, light pollution-free sky to the north — that's the most important direction. And remember that patience counts. The aurora follows its own schedule and sometimes takes a while to get revved up and running. It can also arrive later or earlier than forecast or not all. Like fishing you may not get a nibble but at least you're outside enjoying the scenery. As long as activity — brightness, motion, etc. — trends upward, it's worth your while to stick around to see what's coming. I'll post updates on its progress at facebook.com/astrobobking.

Smartphones work surprisingly well for northern lights photography. If you have an iPhone, just point it at the sky. It automatically puts itself in night mode and allows the user to take 3-second hand-held time exposures. That's plenty of time to capture most auroras. Android phone users should their phones to night mode.

There may even be another geomagnetic storm brewing ! On Oct. 3rd, an even larger X9.1 flare erupted from the same sunspot group, region 3942. That could mean another big display in the offing. What a year it's been for aurora watchers!

Now, let's cross our fingers and hope everything happens according to plan!