November 7, 1997 Movies created every six hours!

It's too late for a summer rerun, but we may be in for a repeat.

The sun released a coronal mass ejection - sort of solar burp of electrified gas - early this week in the general direction of the Earth. This could lead to a geomagnetic storm over the weekend, energizing the aurora and expanding it enough to be seen in the mid-latitudes of the United States late at night.

A strong CME this April caused a moderate geomagnetic storm that affected satellites and communications systems. (April's auroral display online!)

James Spann at NASA's Marshall Space Flight Center, said that it's uncertain whether the CME will be a hit or a miss. The CME was observed by telescopes aboard the Solar Heliospheric Observatory (SOHO) on Nov. 3 and 4.

"There's no way to predict this," he said. "It may miss us or it may hit dead on." Spann is a co-investigator for the Ultraviolet Imager (UVI), one of several instruments aboard the Polar satellite. UVI and its companion, the Visible Imager (VIS) will have the best view of the aurora borealis (northern lights) as they look down on Earth's arctic regions.

"If things do get disturbed, we're going to see a brightening of the aurora with a magnetic substorm or possibly even a storm," he said. A storm in this case has no direct influence on Earth's weather, but it could mean rough sailing for satellites and for electrical power systems on the ground.

Spann and other scientists will be watching data from the Wind spacecraft in a special halo orbit that holds it about a million kilometers away on a line to the sun. Among Wind's instruments is a measure of the solar wind's magnetic field. At this writing it points northward, the same as the Earth's magnetic field. If it flips southward, then things will get exciting a few hours later. Scientists also are watching instruments that measure the speed and density of the solar wind.

If the storm arrives, it will be sometime on Saturday, Nov. 7. The Space Sciences Lab at NASA/Marshall generates automatic MPEG movies every six hours, and our UVI web site posts gif images every 7 minutes while the spacecraft is in a favorable attitude for data downlink.

More may be on the way. The GOES-6 weather satellite earlier today recorded a solar flare emitting strongly in X-rays, often an indication of things to come. As one scientist noted in an e-mail to colleagues, "Hold on to your hats!"