Brushfires in the Sky
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April
25, 2000 -- Two weeks ago stargazers around the world were
outdoors in force. The moon, Jupiter, Saturn and Mars were clustered
together in the evening sky on April 6 for a picturesque
display just after sunset. With cameras poised to record
the spectacle, observers were treated to a dazzling show -- but
it wasn't the show they expected! The sky, instead of darkening
as the sun sank below the western horizon, turned vivid red,
then green and shimmering yellow. It was a rare and unexpected
display of aurora borealis seen as far south as Texas and Florida.
"My intent was to capture the crescent moon along with
Saturn, Jupiter and Mars," said Keith Cooley, an amateur
astrophotographer in Athens, Alabama. "The aurora flare
up was sudden and without warning! It was my first observation
ever of such an event."
Right: Keith Cooley captured this photo of the planets
against a backdrop of reddish-colored Northern Lights from his
backyard in Athens Alabama on April 6, 2000, at 8:30 p.m. Central
Daylight Time. (Camera: Cannon AE-1; F-stop: 1.8; film: Polaroid
400 ASA; exposure time: 10-20 seconds)
The celestial display started around 1630 UT on April
6 when a powerful interplanetary shock
wave passed by the Earth. Aurora borealis was observed almost
immediately over Asia and Europe. Auroras, or "Northern
Lights", are usually confined to high latitudes, but this
was the biggest geomagnetic storm in years. By 2000 UT, observers
in central Europe were reporting colorful lights in the sky.
"Aurora
borealis is a rare event in our area, so to see it for the very
first time is impressive -- to see a display like [this was]
really dazzling!" recounted Ron Baart of Warmenhuizen, Holland.
"It was about 10:55 p.m. local time [on April 6] that we
saw a pillar of red light in the northern sky... also green-blue
to white features could be seen dancing in the heavens."
Left: Juergen Rendtel snapped this photo from Marquardt
(near Potsdam), Germany. (camera: f/4, f=20 mm lens; film: Ektapress
1600; exposure time: 15-30 seconds).
By the time night fell over North America, the geomagnetic storm
was beginning to subside, but not before auroras were spotted
in at least 23 states. Reports poured in from as far south as
Florida and as far west as Utah.
"Most of northwest Colorado was cloud-covered the night
of April 6," recalls James Westlake, Professor of Astronomy
at Colorado Mountain College in Steamboat Springs, CO, "so
I took a group of SKY Club members ... west into Utah. We weren't
disappointed. From near Moab, Utah, we watched the pink and green
fountains spurt above the northern horizon for several hours
around midnight!"
In the Big Bend region of Texas, observers at the McDonald Observatory
were surprised when the sky suddenly turned red during a star
party.
"Sometime between 9:30 and 10 p.m. CDT, one of [the Observatory's] Public Affairs staff, Mr. William Wren, was doing a private star party for some folks when he spotted what he at first
In all, Science@NASA has received over 40 pictures of spectacular aurorae from readers who were outdoors on April 6 and 7, 2000. Please see the gallery of images, below.
Nature's Color TV....
Auroral light is similar to the light from a color television.
In the picture tube, a beam of electrons strikes the screen making
it glow in different colors, according to the type of chemicals
(phosphors) that coat the glass. During a display of aurora borealis,
the air glows as charged particles rain down from space along
Earth's magnetic field lines. The resulting color depends on
the type of molecules that the charged particles hit.
Inside the Picture Tube The electrons and protons that rain down on our atmosphere to produce colorful Northern Lights don't come directly from the solar wind. Instead, they follow a more circuitous route through the "magnetotail."
The magnetotail is
an area of space behind the night side of Earth where the solar
wind stretches the magnetic field into a long comet-like tail.
Inside the magnetotail is the "plasma sheet," a region
that's densely populated with ionized gas. Although it's more
than 60,000 km away, what happens in the plasma sheet is crucial
to auroral activity.
This graphic, courtesy of the University of Alaska Geophysical Institute, shows the average auroral oval above the Northern hemisphere. During geomagnetic storms the oval expands so that people farther south can also see the Northern lights. There is a similar oval over the Earth's south magnetic pole. However, most aurorae there occur over uninhabited areas. |
Although auroral lights sometimes seem very low to the ground, they are in fact higher in the atmosphere than the highest of jet planes. The lowest fringes are at least 40 miles above the Earth, while the uppermost reaches of the aurora extend 600 miles above our planet. For comparison, the space shuttle orbits near 190 miles altitude. Only astronauts can fly through the aurora!
Above: A background of distant stars, sinuous and spiky
bands of Southern Lights (aurora australis), and the faint glow
of charged plasma (ionized atomic gas) surrounding the Space
Shuttle Discovery's engines give this 1991 photo from the STS-39
mission an eerie, otherworldly look. [more
from NASA/Goddard's Astronomy Picture of the Day]
Day in and day out, the best places to be for aurora watching
include Fairbanks, Alaska, parts of Eastern Canada, Iceland,
and the Scandinavian countries of northern Europe. These sites
are close to the average auroral oval -- a circular line around
Earth's north magnetic pole where auroral activity is greatest.
The farther you live from the auroral oval, the smaller your
chances of seeing aurora. For example, aurora borealis in the
southeastern United States happens just once every ten years
or so. The last time (prior to April 6, 2000) was during the
great
geomagnetic storm of March, 1989. People all the way down
in the Florida Panhandle enjoyed a display of Northern Lights
that came and went for nearly two days.
The Aurora Watchers Handbook lists the following "Great Geomagnetic Storms" of the 20th century when auroras were seen much farther south than usual. If you have a childhood memory of aurora borealis, it may have come from one of these storms.
- October 31 - November 1, 1903
- September 25, 1909
- May 13-16, 1921
- April 16, 1938
- February 11, 1958
- July 8, 1958
- August 4, 1972
- December 19, 1980
- March 13-14, 1989
Now, of course, April 6, 2000 can be added to the list.
Ready for more?
"[The April 6] storm reached G4 on the Space Weather Scale," says Gary Heckman, a space weather expert at the NOAA Space Environment Center. "For comparison, the great storm of March 1989 would have been a robust G5 for two nights running. So maybe the activity we expect with the solar maximum period is just now heating up."
According to David Hathaway, a solar physicist at the NASA Marshall Space Flight Center, peak levels of geomagnetic activity tend to occur somewhat later than the peak of the sunspot cycle.
"Geomagnetic storms are often triggered by solar wind from coronal holes, which are somewhat more common just after the sunspot maximum," explains Hathaway. "Many people think the solar maximum is specific date on the calendar, but it's not. Solar Max starts in mid-2000 and it will last for a year or so. All during that time, and for a while afterward, we can expect to see more geomagnetic activity than usual."
So there's hope. Southern observers who were clouded out on April 6 might yet see the aurora for themselves. Meanwhile, you can enjoy what others saw on April 6, 2000 by perusing the gallery of images (below). All of the images were contributed by Science@NASA readers.
Aurora
Gallery
Pictures
from Earth and Space during the geomagnetic storm of April 6,
2000
Unless otherwise stated, all images are copyrighted by the photographers.
| Location | Photographer | Images | Comments |
|---|---|---|---|
| Rosemary Hill Observatory, Florida | Francisco Reyes | #1 | Mars, Jupiter, Saturn, the Moon and the Pleiades appear in this image along with a red-colored auroral sky glow. (Camera: 50 mm lens at f 1.7; Film: Kodak 400 ISO; Exposure: 25 seconds) |
| central Alaska | Jan Curtis | #1, #2, more | Stunning photos from an experienced aurora photographer. See Curtis's "Home of the Northern Lights" for more. (Camera: 35mm lens at f/2.0; Film: Kodak PJ-800 negative print film; exposure: 10 sec) |
|
Muirsheild Country Park, Lochwinnoch, Scotland | Ian Law | #1, #2, #3, #4 | Multicolored aurora. Picture #4 displays a striking ray pattern. |
| McDonald Observatory, Texas | William Wren | #1 | Photographed with a digital camera at 9:30 p.m. CDT on April 6, 2000; shows an observatory dome silhouetted against red aurora. |
| Baker Lake, Washington | Wade B. Clark | #1, #2 | Pretty pictures of Orion against a red aurora. (camera: 28 mm f1.8 wide angle lens; film: Fuji NHG II 800 speed color negative; exposure: 45 to 50 seconds) |
| Hamilton, Washington | Wade B. Clark | #1 | Camera info. same as above |
| Earth Orbit | The Ultraviolet Imager on NASA's Polar Satellite | #1, #2 | These false-color images show ultraviolet radiation from Earth's northern auroral oval less than one hour after an interplanetary shock wave triggered the geomagnetic storm on April 6, 2000. |
| Dirksland, The Netherlands | Corne Donkersloot | #1, #2 | Red and green-colored sky glow. |
| Calder Vale, England | Stuart Whiteley | #1, #2, #3 | Red and green-colored auroras with ray structures. |
| Varese, Italy | Salvatore Furia | #1 | Red sky glow above the Observatorio Astronomico G.V.Schiaparelli |
| Moab, Utah | James Westlake | #1 | "From near Moab, Utah we watched the pink and green fountains spurt above the northern horizon for several hours around midnight." -- James Westlake (Camera: Nikon FE-2, 50 mm lens at f1.8; film: Kodak Max 400; exposure: 20 s) |
| Gray, Tennessee | Mark Marquette | #1 | Pink- and purple-colored aurora with the constellations Orion and Taurus in the background. (camera: Nikkormat EL, 28mm Sigma lens @ f.2.8; film: Fuji 800; exposure: 8 s.) |
| Utrecht, Netherlands | Robert Wielinga | #1, #2, more | Photo #1 shows the April 6 planetary conjunction just before the onset of the auroral storm. Photo #2 shows the Big Dipper awash in the red glow of the aurora. More images can be found at Wielinga's web site. |
| Glengarnock, Ayrshire, Scotland | Tom McEwan | #1, #2, more | Photo #1 shows aurora with striking red-green rays. Photo #2 shows green "coronal" structures. (Camera: 28mm lens @ f2.8; film: Fuji print film; exposure 5-10 secs on 800 ASA) |
| Banchory, Scotland | Darren
Moody (a member of the Aberdeen District Astronomical Society) | #1, #2 | Pictures of red and green aurora with ray structures; buildings and trees in the foreground. (Camera: 28mm lens at f3.5; film: 800 ASA Fuji Superia; exposure time: 5-8 secs) |
| Hampshire, Prince Edward Island, Canada | Garth Arsenault | #1, #2, #3 |
Colorful aurora along with some familiar winter
constellations -- Orion, Taurus and Canis Major. (Camera: Canon
AT-1 using a 28mm lens, wide open aperture; film: Fuji 200 color print film; exposure: 20 - 30 secs.) |
| Fleet, north Hampshire, United Kingdom | Grant Privett (Shropshire Astronomical Society) | #1, #2 | (Camera: Praktica SLR 50mm, F1.8 lens; film: Konica 200ASA; exposure: 15s) |
| Wirral, Cheshire, England | Dave Thomson | #1, more | Reddish-pink aurora and the Big Dipper. (Camera: 28mm F2.8; film: 200ASA; exposure: 15 s) |
| Bardowie, Scotland | Eileen McLaughlin | #1, #2 | Subtle blue and red streamers. "It's the first time I've ever seen an aurora - worth waiting 40 years for!" -- Eileen McLaughlin |
| Athens, Alabama | Keith Cooley | #1, more | Orange-red sky glow with the Moon, Jupiter, Mars and Saturn in the background. |
For more information about geomagnetic storms, visit the NOAA Space Environment Center web site or SpaceWeather.com.
Web LinksNOAA Space Environment Center -official forecaster of space weather events
SpaceWeather.com -daily updates and news about
solar flares, coronal mass ejections and geomagnetic activity
More
about the "magnetotail" and what causes aurora
- from the NASA/Goddard Space Flight center
All about aurora - from the University of Alaska Geophysical Institute
Aurora FAQ - from the University of Alaska Geophysical Institute
Thursday's Classroom -- lesson plans and educational activities about space weather.