The aurora is a bright glow observed in the night sky, usually in the polar zone. For this reason some scientists call it an “aurora polaris”. In northern latitudes, it is known as the aurora borealis, which is named after the Roman goddess of the dawn, Aurora, and the Greek name for north wind, Boreas.

The aurora borealis is also called the northern lights since it is only visible in the North sky from the Northern Hemisphere.

The aurora borealis most often occurs from September to October and from March to April. Its southern counterpart, aurora australis, has similar properties. Australis is the Latin word for “of the South”.

How do Auroras Occur?

Auroras are now known to be caused by the collision of charged particles (e.g. electrons), found in the magnetosphere, with atoms in the Earth’s upper atmosphere (at altitudes above 80 km).

These charged particles are typically energized to levels between 1 thousand and 15 thousand electronvolts and, as they collide with atoms of gases in the atmosphere, the atoms become energized. Shortly afterwards, the atoms emit their gained energy as light.

Light emitted by the Aurora tends to be dominated by emissions from atomic oxygen, resulting in a greenish glow at lower energy levels (at a wavelength of 557.7 nm) and at higher altitudes the dark-red glow (at 630.0 nm of wavelength).

Northern Lights and Folklore:

Since time immemorial, through different cultures and whenever they occur, there have been many beliefs about the northern lights. The Inuit around Hudson Bay had the following explanation of what they saw:

“The sky is a huge dome of hard material arched over the flat earth. On the outside there is light. In the dome there are a large number of small holes, and trough these holes you can see the light from the outside when it is dark. And trough these holes the spirits of the dead can pass into the heavenly regions. The way to heaven leads over a narrow bridge which spans an enormous abyss. The spirits that were already in heaven light torches to guide the feet of the new arrivals. These torches are called the northern lights.”

In Middle-Age Europe, the northern lights were thought to be reflections of heavenly warriors. As a kind of posthumous reward, the soldiers that gave their lives for their king and country were allowed to battle on the skies forever. The northern lights were the breath of these brave soldiers as they resumed their fight in the skies.

Otherwise the northern lights were a sign of omen. They warned of illness, plague and death. When red, which is the most common colour at low latitudes, they signalled the outbreak of war.

No such omens are known in North Norway. Up here, people’s conceptions were more characterized by awe for this mighty phenomenon. One should tread carefully and in no way should the northern lights be intimidated by waving, whistling, staring or any other form of defiane.

Read More about the Folklore

Resources:

A Guide to Auroras

Aurora Borealis

A Page on Auroras

Information on Auroras

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Tags: Astronomy, Aurora, Northern hemisphere