Red Aurora

Early on the morning of December 19, 1980, a blood-red auroral arc suddenly appeared in the skies over British Columbia, Yukon Territory and Alaska. Because of the hour--the event started about 6:20 am, Pacific time, 4:20 am Alaska time--not many people were up to see it, even though it lasted for some time and was seen in central Alaska as late as 7:00 am.

Totally-red auroras occur infrequently, not more than a few have been seen in this part of the world during the last twenty years. The most widely-seen in North America in recent times was the spectacular red aurora of February 11, 1958. That night the sky over almost all of the continent was clear, so millions of Americans and Canadians, even those as far south as Florida and southern California, saw this beautiful display. All night long, the Alaskan sky was filled with red aurora so bright it made the snow on the ground look red.

All-red auroras are seen near the beginnings of large magnetic storms, and only during some of these. At such times, large numbers of electrons originating on the sun stream into the high atmosphere. There they strike oxygen atoms resident at altitudes 200 to 500 km and cause them to emit quanta of pure red light. Normal green auroras and green auroras tinged with reddish lower borders occur at much lower altitude, typically near 100 km. The electrons that produce these auroras are more energetic than those creating blood-red auroras so they penetrate more deeply into the atmosphere. During their passage through the upper reaches, these electrons also cause red emissions from oxygen atoms but the red color usually is so much weaker than the green that it is detected only with special instruments.