If you didn’t see it yourself, by now you have heard about the amazing display of northern lights that occurred on evening of Nov 7th. Nearly everyone in the United States and Canada that had clear skies on that evening was treated to a display that was more than just a few green streaks in the northern sky. No, this display covered nearly two-thirds of the sky and consisted of moving curtains of white, green and red.
The northern lights are also called the aurora. This name comes from the Roman Goddess of the dawn. In the northern hemisphere, they are called aurora borealis or northern lights. In the southern hemisphere they are called aurora australis or the southern lights.
The auroras are caused by the sun. Frequently the surface of the sun has violent storms that spew out streams of charged particles (plasma) in an event called a coronal mass ejection. The results of the storms are solar winds traveling at speeds of 1 to 2 million miles per hour which are filled with tiny highly charged particles.
It takes two or three days but eventually the solar wind reaches the earth. When the particles do arrive, they are deflected towards the earth’s North and South poles by the earth’s magnetic field. When the particles hit and interact with molecules in our atmosphere the particles become excited and begin to glow.
The delicate colors of the auroras depend on the height at which the energy particles collide with our atmosphere. Street lamps and neon signs emit different colors of light depending upon the types of gas trapped within the fixture. The same applies for the auroras. If the predominant gas is oxygen and nitrogen the auroras will be red. This is rare and only occurs at times of maximum solar activity. The most common color is green, and yellow again caused by oxygen, but at lower levels.
The auroras occur on 27 day intervals and usually last for several nights in a row. Northern lights that occur just after dark are not very showy. The best displays occur around midnight or shortly after. The auroras are never absent from the earth. Every hour of the day, every day of the year, the auroras are blazing somewhere on the earth. However, most people can go many years between seeing the northern display. The reason is the aurora spends most of its time around the ends of the earth, where there are plenty of penguins and polar bears but few humans.
The best place to view the aurora lights lay within an auroral zone that encompasses the northern polar regions. From Alaska through the Northwest Territories of Canada, around to Norway, Russia and back to Alaska. Along this band, the lights can be seen on virtually every cloudless night from autumn to spring. Small expansions of the auroral zone are common and aurora often spills out to neighboring regions such as our or in the case of the display last week the entire US. Until next time…