#52 - The Northern Lights

Photo of the northern lights (aurora borealis), taken by my daughter on October 1st, 2025 in north-central Montana.

Right: This image was taken by the Polar satellite on September 22, 1996. The yellow dot represents the geographic North Pole and the red dot marks the position of the Magnetic North Pole. On this night the lights may have been visible over Montana. However, they would not have been visible during the daytime due to the brightness of the sun.

Many people used to think that sunlight reflecting off of ice at the poles causes the northern lights. This is not true! The true cause of the lights is a combination of three factors - the solar wind, Earth's magnetic field (magnetosphere), and the atmosphere.

The solar wind . . .
The sun is constantly emitting charged particles. This invisible "wind" of particles, called plasma, varies in intensity depending on how active the sun has been. If there is some sort of flare or other type of "storm" on the sun, the solar wind becomes stronger.

Earth's magnetic field . . .
We are protected from the harmful effects of the solar wind by Earth's magnetic field. The magnetism of our planet forms an invisible shield represented by the blue lines (pipe cleaners) on the model below. Notice on the image on the right that the lines of magnetism form a circle (or oval) centered around the Magnetic North Pole (red dot).

Earth's atmosphere . . .
As the solar wind encounters our magnetic field, the field guides some of the charged particles down toward the Earth. As the particle enter our atmosphere, something similar to what happens in a fluorescent light bulb takes place. The charged particles energize gases in the atmosphere, causing them to emit light. The normal position of the auroral oval is far to the north of Montana. The city best positioned to see the light show may be Fairbanks, Alaska. As long as the night is dark and clear, there is a very good chance that residents of central Alaska will see the lights. A similar ring of light exists near the Magnetic South Pole (the southern lights; Aurora Australis).

What does it take for us to see the lights in Montana? . . .
The image on the right shows the "normal" position of the lights. In order for the oval to be present over the Big Sky state, something extraordinary must happen on the Sun. There must be a burst of charged particles called a "coronal mass ejection" (CME) and those particles must travel in Earth's direction. CMEs originate from sunspots. When these CME's reach Earth, they can disrupt our magnetic field, causing those invisible lines of magnetism (blue lines on model) to enter the Earth much farther to the south of their normal position. This happens more often during a "solar maximum": a year when the sun is especially active (many sunspots, flares, CME's). Recent solar maximums occurred in 2001, 2013-2014, and 2024-2025.

Term: geomagnetic storm

Below: This model, made with a styrofoam sphere and pipe cleaners, shows the relationship between the magnetic field (blue lines) and the auroral oval (yellow ring).