Few natural phenomena are as breathtaking as the aurora borealis. Here is the real science behind the lights, and where you can still see them today.
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On clear nights near the polar circles, the sky sometimes ripples with color: waves of green, pink, and violet moving slowly overhead. This is the aurora borealis, or northern lights, one of the few natural events that looks almost unreal even when witnessed in person. Despite its otherworldly appearance, the phenomenon has a precise scientific explanation rooted in solar physics.
What Causes the Northern Lights?
The aurora begins on the Sun, not on Earth. The Sun constantly releases a stream of charged particles called the solar wind. When this stream reaches Earth, most of it is deflected by our planet's magnetic field. However, near the North and South Poles, the magnetic field lines curve down toward the surface, funneling some of these particles into the upper atmosphere.
As the charged particles collide with oxygen and nitrogen molecules roughly 100 to 300 kilometers above the ground, they transfer energy to those molecules. The molecules briefly enter an excited state, and as they return to normal, they release that energy as light. Billions of these collisions happening at once create the glowing curtains we see from the ground.
Why the Aurora Has Different Colors
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The color of the aurora depends on which gas is struck and at what altitude:
- Green, the most common color, comes from oxygen molecules at lower altitudes, around 100 to 150 kilometers up.
- Red appears when oxygen is struck at much higher altitudes, above 200 kilometers.
- Blue and purple come from nitrogen molecules, usually appearing at the lower edge of the display.
The intensity and speed of the display depend directly on solar activity. During periods of high solar activity, known as solar maximum, auroras become brighter, more colorful, and visible at lower latitudes than usual.
Where and When to See Them
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The best viewing locations sit inside the auroral oval, a ring-shaped zone around each magnetic pole. This includes northern Norway, Iceland, Finland, Alaska, and northern Canada. The Southern Hemisphere has its mirror equivalent, the aurora australis, visible from parts of Antarctica, southern New Zealand, and Tasmania.
Clear, dark skies away from city lights give the best chance of visibility, and activity tends to peak during the equinox months of March and September, when Earth's magnetic field aligns more favorably with the solar wind.
A Phenomenon Still Being Studied
Even with centuries of observation, scientists continue to refine their understanding of auroras. Space agencies now track solar activity in real time, allowing researchers, and aurora chasers, to predict displays days in advance with increasing accuracy.
Scientific Sources
- NASA, "Aurora"
- NOAA Space Weather Prediction Center
- European Space Agency, "What Causes the Northern Lights"
