On August 1, 2010, American astronomers observed the sun emit a series of four large coronal mass ejections. A coronal mass ejection, also known as a "solar flare," is a powerful eruption of electromagnetic energy from the surface of the sun into the outermost layer of the sun called the corona. It looks like a series of gigantic fountains of fire issuing from the entire surface of the sun. The largest coronal mass ejection may have a temperature of up to 4 million degrees Fahrenheit and extend more than one billion miles from the solar surface into space.
These eruptions are associated with sunspots, magnetically polarized regions of the sun's surface that are ironically cooler than the surrounding surface area, often having temperatures of only 10,000 degrees F. A coronal mass ejection sends a concentrated stream of electromagnetically charged particles into space that can travel for many millions of miles. When these particles collide with earth, they interact with the planet's magnetic field in the exosphere --the outermost layer of earth's atmosphere -- high above the north and south poles, generating beautiful displays of colored lights in the polar night skies known in the Northern Hemisphere as the aurora borealis, or northern lights. A large solar flare may even cause the northern lights to be seen at temperate mid-northern latitudes, although the display will be significantly dimmer and more subtle here.
Such bursts of solar energy are a regular feature of the sun, but every so often an unusually powerful burst will occur. NASA's Solar Dymanics Observatory, a spacecraft launched to study the sun, recorded four such bursts on August 1. These coronal mass ejections, traveling at speeds of over 1 million miles per hour, reached the earth three days later on the evening of August 4. The result was a spectacular aurora borealis display over earth's northern polar regions. The show extended as far south as the 45th parallel of latitude, and was seen by people in the northern United States.
Because coronal mass ejections occur at irregular intervals, astronomers cannot predict their occurrence. However, a large solar flare is an event typically observed by astronomers once
every one and a half years. Previous such events occurred in 2008, 2005 and 2003.
When you hear about a large solar flare in the news, check the night sky in the days following the event to see if you can see an auroral display. Be sure to observe from a location with a dark sky and an unobstructed northern horizon.
I myself have seen the aurora borealis on two separate occasions from my home in Ohio. The first was in October 2003, when I saw a green glow above the horizon and observed subtle red curtains of light waving high in the northern sky. My second sighting was of an even more subtle event in May 2005, when I merely noticed that the usual yellowish-white glow of distant city lights bore a greenish tinge. Although neither show was spectacular compared to the displays visible in polar regions, I was thrilled to be able to see them because of their rarity at midnorthern latitudes and because they were the first two times I ever witnessed the aurora borealis. I missed out on seeing the most recent extraordinary auroral event because I did not live far enough north to see it, but I will keep my eye open for future such events.
Copyright © 2010 by Justin Soutar. All rights reserved. This article may not be reproduced without the written permission of the author.