North through British Columbia - Alaska and Points North: Tips and Tales from the Road - page 59

Interesting Info:
The Northern Lights
What causes them?
The lights are the result of collisions between electrically charged particles from the sun that
enter the earth's atmosphere.
Why the difference in colours?
The variations in colour are due to the type of gas particles that are colliding.
Green: Oxygen molecules at about 60 miles above earth.
Red: Red auroras are caused by oxygen at higher altitudes - up to 200 miles.
Blue or Purplish: Nitrogen molecules
Best place to see them?
Because the earth's magnetic field is weaker at its poles, the particles from the sun are able
to enter the earth's atmosphere there. The aurora can be seen in either the north or south-
ern atmosphere as an irregularly shaped aurora oval, centred over each magnetic pole. In the
north, the lights are known as the Aurora Borealis and in the south they are known as the
Aurora Australis.
The most reliable locations for a good sighting in North America are in north-western
Canada, particularly the Yukon, Nunavut, Northwest Territories and Alaska. Small com-
munities with few lights are the best locations.
The southern auroras are not often seen by people because they are concentrated in a ring
around the unpopulated Antarctica and south Indian Ocean.
Best time to see them?
Aurora activity is cyclic, peaking every 11 years or so. They are visible between peak years,
but the next peak period is 2013. Winter in the north is the best time because of the clear
nights and long periods of darkness.