Understanding the Northern Lights Colors
The aurora borealis primarily appears near the north and south poles and is caused by charged particles from the sun. When these particles collide with gases in Earth's atmosphere, they cause spectacular color displays. The key players here are oxygen and nitrogen, which create different colors depending on the altitude of the collisions.
For example, oxygen molecules can emit a vibrant green light at altitudes of about 30 miles. At higher altitudes, around 60 miles, nitrogen can produce blue or purple hues.
Most auroras occur during times of heightened solar activity, and that heightened activity is what can bring the aurora further south, and visible in places like northern Michigan. Here is how it happens........
Solar Flares
Photo courtesy of thewondersofscience.com
Solar flares are sudden bursts of energy on the sun's surface. They form from a complex process around sunspots, areas with intense magnetic activity. When the magnetic fields linked to these sunspots rearrange, they unleash a tremendous amount of energy in just minutes—more than the total energy produced by Earth in a year.
During these flares, the sun can unleash energy (Coronal Mass Ejections) equivalent to billions of megatons of TNT. The electromagnetic radiation emitted then travels through space and interact with Earth's magnetic field, leading to those eye-catching auroras in polar regions.
Solar flares vary in strength. They are classified into different categories, with X-class flares being the most powerful, M-Class a mid-range flare, and C-class being a minor flare. On October 9th, 2024 an X-class flare (with CME) was responsible for an aurora display seen as far south as Cuba. (These are the flares we want!)
Coronal Mass Ejections (CME's)
CMEs are large expulsion of plasma and magnetic fields from the sun's corona, resulting from a solar flare, capable of reaching speeds up to 3 million miles per hour. It can take hours or even days for these giant clouds to reach Earth.
When a CME collides with Earth’s magnetosphere, it can result in geomagnetic storms. Such storms often intensify the northern lights, allowing them to be visible even at lower latitudes. For instance, the X-class flare mentioned above resulted in a direct hit from a massive CME, allowing the aurora to be seen by much of the world.
The following video shows how it all works.....
Courtesy University of Oslo
Coronal Holes
Solar Flares that produce CME's directed at earth are responsible for the strongest aurora displays. However, coronal holes can also produce a decent display.
Coronal holes are regions in the sun's outer atmosphere where the magnetic field opens up and allows solar wind to escape into space. These areas appear darker in ultraviolet and X-ray images due to lower temperatures and densities compared to the surrounding regions. When facing earth, coronal holes often create accelerated solar wind, which can in turn create aurora.
Solar Cycles
Scientists have discovered the sun has active periods, and periods with less activity. Approximately every 11 years the sun's activity reaches what is called solar maximum. This period of heightened activity lasts for approximately 1-2 years. During this time period, and especially around the fall equinox, is the best time to see the northern lights. As I write this blog post, we are currently at solar maximum, as confirmed by NOAA's Space Weather Prediction Center. SO RIGHT NOW (until 2026ish) IS THE PERFECT TIME TO CALL AND BOOK A "NORTHERN LIGHTS IN THE KEWEENAW TOUR, focusing on photographing the aurora for beginners.
Simple Summary
1) The aurora is caused by the sun's activity, so watch for solar flares that produce a CME that is directed at earth.
2) The colors are a result of particles from the sun that crash into the different elements of earths atmosphere.
3) Large, earth facing coronal holes can produce aurora, though most likely at higher latitudes.
4) Solar activity heightens approximately every 11 years. This is called Solar Maximum. The aurora occurs more often during these times.
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