Oct 22, 1999

Aurora Alert





A blast of solar wind from the sun on October 21 is creating strong geomagnetic storm conditions a day later


polar UVI animation of an aurora over the northern US
Oct 22, 1999: At 9:00 a.m. MDT (1500 UT), NOAA's Space Environment Center reported that a strong geomagnetic storm was in progress. The storm is possibly the result of a shock observed in the solar wind on Oct 21 at 01:38UT (Oct 20 at 07:38 p.m. MDT), originating from a mass ejection on the Sun Oct 18. The shock front struck Earth's magnetosphere around 0240 UT on October 21.


The Ultraviolet Imager on NASA's polar spacecraft captured dramatic images this morning of an aurora borealis in progress over the northern United States. Aurorae -- sometimes called Northern Lights -- are luminous multi-colored curtains of light most often seen in the skies at very high northern and southern latitudes. They occur because Earth's magnetic field interacts with the solar wind, a tenuous mix of charged particles blowing away from the sun. Auroral light results from electrons and protons striking molecules in the Earth's upper atmosphere.

Right: These images were captured by the Ultraviolet Imager on NASA's Polar spacecraft's on Friday, October 22. They show UV emissions from aurora borealis during a strong geomagnetic storm. Click for a

. For movies of last night's aurora as seen by the visible camera on Polar click here.




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"This storm is notable, at least for us Americans, because it's producing aurora over the contiguous 48 states," said NASA/Marshall's Dr. Jim Spann a co-investigator on Polar's UVI instrument. "By 0704 UT the storm was going pretty strongly over the Hudson Bay and surrounding areas, and a few minutes later it was south of the 48th parallel. Anyone who was out looking at the sky over the Great Lakes at 2am might have seen some beautiful lights."

Indeed, it appears that many observers did spot the Northern Lights early this morning. The Solar Terrestrial Dispatch reports widespread sightings ranging from Washington State in the west to New York in the east, and as far south as Ohio. Click for the latest reports.

Gary Heckman, a space weather forecaster at NOAA's Space Environment Center says it's hard to predict whether the auroral activity will continue through the night of October 22, but for residents of the northern US it's worth taking a look. Tonight's bright full moon could make faint auroral emissions difficult to see, but strong auroral activity might be visible despite lunar interference. The best time to observe is near local midnight.


Parents and Educators: Please visit Thursday's Classroom for lesson plans and activities related to this story.


see caption
Right: What does an aurora look like? This colorful picture taken in January 1998 shows a spectacular aurora borealis above a frozen landscape of snow-covered spruce trees in Alaska. Auroral light results from solar electrons and protons striking molecules in the Earth's atmosphere. Aurorae rarely reach below 60 kilometers, and can range up to 1000 kilometers. Frequently, when viewed from space, a complete aurora will appear as a circle around one of the Earth's magnetic poles. [Picture credits]


For more information about space weather and current solar activity, including official alerts, warnings, and forecasts, please see NOAA's Space Environment Center web site at


Web Links


Movies of last night's aurora as seen by the visible camera onboard POLAR

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Author: Dr. Tony Phillips
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