Auroras may dazzle more people than usual this weekend as Earth receives a glancing blow from an enormous solar outburst that erupted on Jan. 19.
The outburst, known as a coronal mass ejection (CME), was detected by sun-watching satellites.
Researchers at the University of Alaska's Geophysical Institute predict that auroras should be visible from Seattle, Des Moines, Chicago, and Cleveland, to Boston and Halifax, Nova Scotia Saturday and Sunday nights, weather permitting.
Space-weather forecasters initially were concerned that Earth would take a direct hit, notes Joe Kunches, a space scientist at the National Weather Service's Space Weather Prediction Center in Boulder, Colo.
"Indications at the time were that this could be a fairly energetic event," says Mr. Kunches, a former operations chief at the center. The solar flare that triggered the coronal mass ejection covered a relatively large patch of the sun and released a lot of energy. Where other flares during the week lasted an hour or two, the flare that launched the CME lasted roughly 18 hours.
And the CME "was in the right spot," he adds. It emerged from just about the middle of the sun's disk.
It's the "just about," however, that led to the prediction of a glancing blow, rather than a direct hit. The CME emerged from a location just north of the sun's equator, so for the most part it will hurtle past Earth far above the North Pole.
Space Weather Center forecasters say they expect the encounter to generate a weak geomagnetic disturbance beginning around 1 p.m. Eastern Standard Time Sunday Jan. 22 and lasting through Jan. 23. It could trigger weak fluctuations in electricity flowing through the long-distance transmissions lines and have a minor effect on satellites.
Coronal mass ejections represent the sudden release of a vast, searingly hot cloud containing up to 200 billion tons of electrons and protons, as well as heavy atomic nuclei forged in the sun's nuclear-fusion furnace.
Hurtling from the sun at speeds of up to 2 million miles an hour, CMEs can generate intense disturbances in Earth's magnetic field that can trigger power and radio blackouts and disable satellites – as well as generate spectacular aurora over the North and South poles.