Photograph by Roy Samuelsen, My Shot

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An aurora glimmers over Norway in a 2008 picture.

Photograph by Roy Samuelsen, My Shot

Solar Storm Headed for Earth Tonight; May Spawn Auroras

A huge eruption on the sun may trigger auroras tonight, and the light show could be more widely visible than normal, astronomers say.

Night owls take note: A spectacular sky show of rippling auroras may be on tap for late Tuesday through early Wednesday, according to astrophysicists, and the phenomenon may be more widely visible than normal.

On Sunday cameras aboard NASA's Solar Dynamics Observatory (SDO) captured an eruption on the sun's surface that hurled tons of plasma—charged gas—directly toward our planet in an event called a coronal mass ejection. (See sun pictures taken by the solar observatory.)

Watch a brief NASA video of the August 1 sun eruption, as seen by the SDO:

Because it takes several days for such ionized clouds to reach Earth's atmosphere, the burst of charged particles should hit us tonight—and there's a chance it'll produce especially colorful auroras.

Auroras happen when energized particles from the sun interact with Earth's magnetic field. The particles flow down the field lines that run toward Earth's Poles, banging into atoms of atmospheric nitrogen and oxygen along the way.

The charged solar particles give Earth's atmospheric atoms an energy boost, which then gets released as light, producing the shimmering curtains of greens, reds, and other colors.

In the Northern Hemisphere, auroras are more commonly seen at high latitudes, such as the Arctic regions of Alaska, Canada, and Scandinavia.

But explosions like Sunday's can spark geomagnetic storms that bring the show to slightly lower parts of the globe. These storms can also add a rippling effect to the sometimes static auroras.

Still, a solar storm headed for Earth isn't a guarantee of auroras. Without more sun-watching satellites, scientists are hard-pressed to know the exact effects a coronal mass ejection will have on Earth's atmosphere.

For now, the odds of auroras lighting up tonight's northern skies are about 50-50, said Leon Golub of the Harvard-Smithsonian Center for Astrophysics.

If you want to watch for them, he advised, "find a dark place and look north well after sundown or near midnight, if you can stay up that late."

Sun Probes to Issue Space Weather Alerts?

The oncoming solar storm is yet another indicator that the sun's activity is picking up after an unusually long lull, astronomers say.

Solar activity rises and falls on a regular cycle of about 11 years. The last period of peak activity ended in 2001, and it led into a long-lasting quiet spell. (See "Sun Oddly Quiet—Hints at Next 'Little Ice Age'?")

Along with a recent flurry of sunspots, Sunday's eruption seems to be a sign of the star's reawakening—good news for aurora fans, but potential trouble for satellites, astronauts, and some technologies here on Earth.

Energetic solar storms can disrupt communication and navigation systems, can knock out power grids, and can pose radiation hazards to people working in space.

This week's storm is relatively slow, which means it's unlikely to have many negative impacts—but future storms probably will, Golub said.

"One of the main reasons to have these instruments [such as the Solar Dynamics Observatory] in space is so that you can issue alerts or warnings, pretty much like you would with a hurricane," he said.

That way "people can know ahead of time when there is a possibility of an event that will have an impact on Earth."