Aurora Basics
Aurora Borealis and Northern Lights are two terms for the same phenomenon occurring in
the Northern Hemisphere. Because the earth has two auroral ovals centered on the earths
geomagnetic poles, this phenomenon also occurs in the South Hemisphere known as the
Aurora Australius or Southern Lights.
When is the best time of year to see the Northern Lights?
Northern Lights can be visible ANY time during the year. There is no "best time." Because
Minnesota has longer nights during the winter, sometimes more people see Aurora during
the winter months, but there have been shows in June and July that have been visible, as
well.
What causes the Northern Lights?
Years ago people believed that the auroras were caused by sunlight reflecting off the
polar ice pack. Another belief was that auroras were caused by sunlight reflecting off
ice crystals in the air. Neither theory was true. As technology improved, it was soon
discovered that northern lights and sunspot activity were closely related.
Periodically our sun develops sunspot areas that to the eye appear to be a spot or pimple on its
surface. A spot may grow until, like a volcano, it explodes and spews gases and particles
away from the surface of the sun. Because the sun has no atmosphere to hold the particles
back, these electrons and protons stream away from the sun. If the earth is in line with
the explosion, the particles race toward the earth and excite the earth's magnetosphere,
causing the aurora. The interaction with the various gases in earth's magnetosphere
determines the color of the lights.
For a simpler explanation, think of the earth as if
it is a neon light bulb. When the charged particles from the sun hit the earth's
magnetosphere, it lights up just like the neon light bulb lights up when electricity is
passed through it.
Why don't we always see the Aurora?
Certain factors must be present for the Northern Lights to appear:
- Sufficient activity from the sun to excite the earth's magnetosphere (coronal hole flow or a solar flare with a coronal mass ejection)
- Dark observation location
- Clear skies
I've only seen white or whitish-green northern lights. Why are your photos in color?
At low light level the human eye is color-blind and can only see black and white. If an
aurora is weak it won't produce enough light for the cones in our eyes (the color
sensors) to see any visible color. A camera does not have the human eye's limitations and
is able to capture the aurora with the full spectrum of light.
