Aurora Borealis: What the Northern Lights Are and How They Actually Form

Most people know aurora borealis as the northern lights — a natural light display in the polar sky. Fewer know the full chain of events that produces it, from the sun's surface to the ionosphere overhead. Understanding that chain doesn't diminish the experience of watching aurora; it deepens it. The physics behind the light is as remarkable as the light itself.

What Aurora Borealis Is

Aurora borealis is the light produced when energetic electrons, accelerated along Earth's magnetic field lines by field-aligned currents, collide with oxygen and nitrogen atoms in the ionosphere at altitudes of roughly 100 to 300 kilometers. Those collisions excite the atoms to higher energy states; when the atoms return to their ground state, they release the absorbed energy as light — the colors of the aurora, determined by which gas is involved and at what altitude the collision occurs.

The name combines the Latin for dawn — aurora — and the Greek word for north wind — boreas. It was coined by Galileo in 1619, though the lights had been observed and documented by northern peoples for millennia before that.

What helped me picture the mechanism: think of a neon sign. Electricity passes through a gas-filled tube, exciting the gas atoms; when they relax, they emit light at specific wavelengths determined by the gas. Aurora works on the same principle, at planetary scale, with Earth's magnetic field guiding the electrons into the ionosphere the way a tube shapes the path of current in a neon sign.

Aurora Borealis vs. Aurora Australis

Aurora borealis occurs in the northern hemisphere; aurora australis is its southern counterpart. The two are conjugate phenomena — they occur simultaneously along shared magnetic field lines, mirroring each other across the two hemispheres. During a geomagnetic storm visible from Alaska, the same event is producing aurora over Antarctica along the same field lines.

Why Aurora Borealis Matters for Travelers

Aurora borealis is visible from within the northern auroral zone on the majority of clear, dark nights during the winter viewing season. The key variables are darkness — aurora is present year-round but invisible during the midnight sun of polar summer — and geomagnetic activity, which determines how bright and active the display will be on any given night.

Fairbanks, Alaska sits beneath the auroral oval and offers some of the most consistent aurora borealis viewing accessible by commercial travel. The combination of geography, darkness window, and statistical frequency of clear nights makes interior Alaska one of the most reliable destinations for experiencing the northern lights. Our Northern Lights Tour in Fairbanks is designed around exactly these conditions. For more on timing, see our guide on the best time to see the northern lights in Alaska.

What Aurora Borealis Means for Photographers

For photographers, aurora borealis presents a subject that is simultaneously predictable in its broad patterns and completely unpredictable in its moment-to-moment behavior. The colors are determined by atmospheric chemistry — green from oxygen at 100–150 km, red from oxygen above 200 km, blue and purple from nitrogen below 100 km — and those relationships are consistent. What isn't predictable is when a substorm will fire, how fast structure will move, or whether the sky will be clear.

The most photogenic aurora borealis tends to occur during substorm onset — when structure rapidly develops from a quiet arc into moving curtains and potentially a full-sky corona. Wide-angle lenses in the 14–24mm range on full-frame cameras are standard for capturing the full extent of overhead structure. Exposures of 3–15 seconds depending on activity level, ISO 1600–6400, and apertures of f/2.8 or wider are the typical starting parameters.

Return to the full Northern Lights Glossary to continue through the Aurora Visual Forms and Phenomena section.