Names and Definition of the Aurora
The Northern Lights and the aurora borealis are two names for the same thing. The term aurora borealis was first used by Galileo in 1619 to suggest the likeness of the northern lights to an early dawn in the northern sky, an appearance it sometimes has to those who live at low or intermediate latitudes in the northern hemisphere.
Once the term aurora borealis was introduced, Galileo and others used it as the name for the Northern Lights. The early history of auroral terminology is somewhat clouded because, at the time, Galileo was already under duress from the Roman Inquisition and was not supposed to be writing on astronomical matters. Therefore, his writings on the subject were appearing under the name of his student, Mario Guiducci. Galileo referenced the aurora as part of his arguments against the established idea that the earth was the center of the Universe. He wrongly thought that the aurora is caused by sunlight reflecting from the high atmosphere.
Galileo's original error has propagated through nearly four centuries to the present time. Misinformed by geography books written as late as fifty years ago, a surprising number of people still labor under the misconception that the aurora is sunlight glinting off the high atmosphere, off the polar icecap or off falling snow or ice crystals.
Instead, the aurora is an actual light source created in the high atmosphere. It is a glow given off by the atoms and molecules of which the atmosphere is composed. That glow is caused by the atoms and molecules being struck by charged particles, mostly electrons and protons, that originated on the sun. These particles stream out from the sun and normally are guided by the earth's magnetic field into the polar regions where they enter the atmosphere and make it glow.
The proper name for the aurora of the southern hemisphere is the aurora australis. Together the aurora australis and the aurora borealis are known as the aurora polaris. Nowadays the simple name aurora is mostly used, as is the name Northern Lights.
