| Home | Articles | Guide to Observing | Tour of the Constellations | Book Reviews |
The above photographed is displayed with permission of NASA.
The Sun does not only send rays of light and heat to the Earth; it constantly bombards the Earth with the Solar Wind consisting of protons and electrons. The Solar wind typically moves a few hundred kilometres per second and consists of several protons for every cubic meter of space. The Earth acts like a giant magnet with lines of electromagnetic force running from the high latitudes of Canada to somewhere in Antarctica. The Earth's magnetic field looks a bit like a giant donut and the Solar Wind can break through this field only at the holes of the donut located near the Earth's poles. The interaction between the protons and electrons of the Solar Wind and the Earth's atmosphere creates a slight glowing in the sky – the aurora – which is usually too dim to see. But occasionally, the Sun emits the Solar Wind in a giant "clump" called a Coronal Mass Ejection (CME) which can travel at thousands of kilometers a second and has a much higher density of particles. When, a massive CME hits the Earth's upper atmosphere a visible display of light occurs which is called the aurora borealis (or the Northern Lights) when seen north of the equators or the Aurora Australis when seen south. There are many different variations of the aurora. It may appear as a green shimmering curtain of light, for instance.
The closer you are to one of the Earth's magnetic poles, the more likely you will see an aurora. The aurora can frequently been seen in Alaska and northern Canada and sometimes near the U.S-Canadian border, but during times of very intense solar activity, it has been possible to see the aurora in even the southern parts of the United States.
More info on the Sun-Earth environment on SpaceWeather.com
Perseus