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The Northern Lights
With Dr. Charles Deehr
University of Alaska's Geophysical
Institute
Tuesday, Feb. 19; 12:30 p.m.
EST
When electrically charged particles from the sun enter the earth's atmosphere and collide they create bright lights over the north and south poles. Known as aurora borealis or the Northern Lights in the north and aurora australis or Southern Lights in the south, these lights have amazed and enchanted people for centuries.
Dr. Charles Deehr, professor emeritus in physics at the University of Alaska's Geophysical Institute, was online to take your questions and comments on the aurora borealis.
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The transcript follows.
Hollandale, Wis.:
What month in the year do these Northern Lights appear & for how long? Lovely images online. Thanks.
Dr. Charles Deehr: The aurora may appear during any month of the year, depending on solar activity. There tends to be more auroras around the equinoxes, i.e., March and September.
Alexandria, Va.:
Just wanted to note the site www.spaceweather.com for anyone who is a real aurora nut like me. Awesome photos on a regular basis from around the world, and early warning of potential aurora displays. I was mesmerized by the Northern Lights during visits to the Bay of Fundy and Newfoundland over the past several years, and I never imagined seeing them close to home until last fall when they appeared on the horizon in full view from my office window in North Bethesda. Maybe it's my First Nations ancestry coming through, but I would swear that they sing to me!
Dr. Charles Deehr: You should drive north to Matagami, Quebec or Waskaganish and enjoy the aurora and your First Nation status. The zone of maximum auroral occurrence frequency is over James Bay (visible every clear, dark night).
College Park, Md.:
When is the best time of the year to view the lights?
Dr. Charles Deehr: The best time of year is the new moon in March. At this time, the skies are clear, and the maximum in yearly auroral occurrence frequency is at the spring equinox (Mar 21). The new moon is on the ides of March this year and this coincides with a recurring fast stream of particles from the sun, so we expect some good activity during these 2 weeks of dark skies centered on the 15th of March.
Alexandria, Va.:
What did the Eskimos think was the cause of the aurora borealis? Were they able to derive any useful information (about navigation, weather, seasons, etc.) from observing it?
Dr. Charles Deehr: Northern Native legends and stories of the aurora are numerous. They have the same role as other natural phenomena that were not understood. As far as I am aware, there was never any practical use made of the lights except perhaps for illumination during moonless periods.
Bowie, Md.:
Can the Northern Lights be predicted in advance?
Dr. Charles Deehr: Auroral prediction is part of what is called space weather prediction. It is approximately 150 years behind meteorology (around 1850, weather data were assembled using the newly invented telegraph). We are just now able to assemble pictures of the sun from satellites showing the two different sources of energy for the aurora: recurring fast streams and sporadic storms. The recurring fast streams create a few days of auroral activity each time they face the earth with the 28 day solar rotation. After a sporadic storm or flare, it takes 2 to 5 days for the particles to reach Earth on the solar wind.
Rockville, Md.:
What's the most southern point in the continental U.S. you have heard reports of seeing the Northern Lights? Also, where in the 48 contiguous is the best place to spot them? I would love to witness this!
Dr. Charles Deehr: We have reports of auroral sightings from every one of the United States. The best places are in the northern tier in March on moonless clear nights. Watch the northern horizon from 9 pm to 3 am away from city lights (not so much of a problem in ND, MN, WI, and MI (up). There is no wall at the border though, and your chances increase measureably as you approach an East West line from Watson Lake YT, Fort Nelson BC, Fort McMurray, Alberta, Flin Flon, to James Bay. There they see the aurora every clear dark night. Canadians are cool, the exchange rate is good, but bring your passport to get back across the border.
Arlington, Va.:
The aurora may be the most breathtaking
thing I have ever witnessed. I was in
Montana a couple years ago and saw it
and while it was mostly green there was
some red in there, too. What accounts for
the color variation?
Thanks!
Dr. Charles Deehr: The aurora is light created by energetic electrons striking oxygen and nitrogen atoms and molecules in the atmosphere. These atmospheric constituents each have a characteristic color, just like the different gases in "neon" signs. Depending on the energy of incoming electrons and the condition of the atmosphere and the height of the emission above earth (60 - 600 mi)the aurora can be typically blue, red and green.
Seeing the lights:
Perfect timing, I am planning a vacation up to Alaska soon and my travel partner asked what our chances were of seeing the light. Late August/September in the Kenai Peninsula (south of Anchorage). Any ideas?
Dr. Charles Deehr: The frequency of occurrence falls off considerably between Fairbanks and Kenai. If the weather is good, and we do have clear periods at that time of year, it would be worth your while to drive north 2 days to Fairbanks, or at least to Mckinley Park. If the weather is good in Kenai, you should be able to see aurora on 4 of any 10 clear, dark nights.
Somewhere, USA:
What are the earliest recorded sightings of the aurora? How have people accross the ages reacted to it and when was it first scientifically explained?
Dr. Charles Deehr: There are allusions to what may have been aurora in the Bible (Ezekiel saw a wheel way up in the middle of the sky). Babylonian clay tablets refer to what must have been aurora, but serious discussions of it probably began with the Greeks (Anaximenes, 650 BC). Serious study began with that of astronomy, etc about 1600 AD. Because of a low solar activity during the 17th century, most scientific work began with the occurrence of renewed activity around the beginning of the 18th century. The relation of aurora to geomagnetic disturbances and solar storms was made in the 19th century. That it was produced by incoming energetic particles was proven in 1950, so most of the major discoveries were made in the 20th century.
Washington, D.C.:
I just wanted to share a magical northern lights moment. I was in North Dakota, fighting a flood several years ago and as we left the sandbagging site, we looked up and there were the most spectacular northern lights. We drove out of town a ways and stood for quite some time in the cold, just watching them. There was a comet in the sky then also (Hale-Bopp?). Anyway -- it was a remarkable, serene moment, amidst much chaos in the town.
Dr. Charles Deehr: There are studies of the relationship of geomagnetic disturbances to various human maladies. They rank with climate change in lacking a definitive physical process to explain the trends.
The single most reported effect on human conciousness is that of the fascination and euphoria associated with a chance encounter with this overwhelming, but non-threatening phenomenon. This e-mail from the solar system seems to evoke a feeling of some relationship with a larger, more tranquil universe, at the very least, a significant neurogenisis.
Gainesville, Va.:
I live in Northern Virginia, about 30 miles south west of Washington, D.C. What are the chances that I'll be able to see the aurora borealis in March (you mentioned near the new moon)? What should I do to maximize my chances of seeing them?
Dr. Charles Deehr: From your home, you should drive to a high point with a clear view of the northern sky on a clear moonless night. Usually between 9pm and 3am you would see something on 1 night in 10. You may increase your chances of seeing something by checking the auroral forecast at http://www.gi.alaska.edu.
Chesapeake Beach, Md.:
When a solar event occurs that is likely to cause a major aurora borealis, I understand astronomers frequently know that it's coming a few days ahead of time, since the aurora-causing radiation travels much slower than light.
What's the best way for the layman to know in advance when to look for the aurora borealis? Is there a good Web site to check, or an e-mail list one can get on?
Dr. Charles Deehr: You can now go
directly to the auroral forecast page at:
http://www.gi.alaska.edu/cgi-bin/predict.cgi
or check out more extensive information on the aurora and other arctic
geophysical phenomena at
http://gedds.pfrr.alaska.edu/ and http://www.gi.alaska.edu/
If you can't travel, enjoy some of the other web sites listed, especially pictures by
Jan Curtis
http://climate.gi.alaska.edu/Curtis/curtis.html
Watch
http://sec.noaa.gov/pmap/index.html
and the information on observing the aurora, etc. that are with this page. It shows the world wide extent of aurora during the last hour.
Marquette, (UP) Mich.:
Have enjoyed seeing Northern Lights on quite a few occaisions up here, usually greenish displays. Was thrilled to see the brilliant red display this past November. I understand the color of the Northern Lights is dependent on particular atoms at different elevations being excited by the electromagnetic activity. Can you go over what combinations produce which colors?
Dr. Charles Deehr: The diffuse, blood red near the upper parts of the arcs is from the 6300 A emission line of atomic oxygen. The green is from the 5577 A emission line from atomic oxygen. Most of the molecular emissions combine red and blue with this green to make white or grey, but the occasional blue is due to ionised nitrogen molecules, and the magenta lower border seen on very active auroral arcs is a combination of that blue and the red from molecular neutral nitrogen, and most importantly, the quenching of the most visible green line referred to above.
washingtonpost.com:
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