While all eyes were glued to the tropics during a record-setting September, fall happened! Photos of Colorado aspen trees bright as fire suddenly appeared all over social media, the beautiful maples (among other trees) dotting the northern New England landscape in reds, browns and oranges made us stop and smile, and the first glimpses of the aurora borealis graced our northern sky.

“Magic in North Dakota” — that’s how photographer Carl Jones described this vibrant aurora borealis as it lit up the night sky over North Dakota last week. While we use the calendar to tell us when the various seasons “officially” hit, we can use signs in weather and nature to tell us as well. Most recognize the change in the color of the deciduous leaves as a sign that fall is here, and that it’s time to break out the flannel and pumpkin spice.

The aurora borealis, also known as the “northern lights,” is another telltale sign fall is here with its longer nights. The aurora borealis can be seen year round, but it is most common and most vibrant during winter’s long, clear and dry nights.

Northern lights pop up when electrically charged particles from the sun enter Earth’s atmosphere. When they interact with our atmosphere, the result is a ballet of dancing lights on the northern horizon. While the vibrant lights in the sky seem close, this colorful interaction is actually happening 60 to 70 miles above Earth’s surface, nearly 10 times higher than where commercial airplanes fly. The wispy array of lights can also extend hundreds of miles into space.

In the photo above, notice how green is the dominant color? Why? You can thank oxygen for that! Now, different gases in the atmosphere are responsible for different colors. When the charged particles from the sun hit the atmosphere, different gases emit different colors: Oxygen gives off greens and yellows, while nitrogen emits blues and reds.

So with that said, welcome to fall and all the beauty that comes with it!

Here are a couple more stunning photos of the northern lights last week over North Dakota.