What causes the northern lights?

The northern lights, or aurora borealis, are glowing curtains of light in the night sky near Earth's magnetic poles. They begin at the Sun, which constantly streams out a wind of electrically charged particles called the solar wind. When these particles reach Earth, most are deflected by our planet's magnetic field, but some are channeled along magnetic field lines toward the polar regions. There, roughly 100 kilometers up, they collide with atoms and molecules of oxygen and nitrogen. Each collision transfers energy, kicking the gas atoms into an excited state. Moments later the atoms shed that extra energy as tiny bursts of light. Billions of these emissions together create the shimmering glow we see. The southern counterpart, the aurora australis, forms the same way over Antarctica.

The colors are not random; they reveal which atoms are glowing and how high. The principle is atomic emission: an atom absorbs energy, an electron jumps to a higher orbit, then falls back and releases a photon of a specific wavelength. Oxygen high in the atmosphere emits the familiar green light, and at greater altitudes a deep red. Nitrogen produces blue and purple hues. Because each gas radiates fixed colors, the aurora is essentially the upper atmosphere's fingerprint written in light. The particles ride along Earth's magnetic field, which is why auroras cluster in oval-shaped bands around the magnetic poles rather than appearing everywhere. When the Sun is especially active, stronger gusts of solar wind push those ovals toward the equator, and the display grows brighter and spreads farther south.

Auroras rise and fall with the Sun's roughly 11-year activity cycle, and forecasters now track them closely. The U.S. National Oceanic and Atmospheric Administration runs a Space Weather Prediction Center that monitors solar storms and issues aurora forecasts days ahead. This matters beyond tourism: the same eruptions that brighten the sky, called coronal mass ejections, can induce currents in power lines, disturb GPS signals, and damage satellites. A famous 1859 storm known as the Carrington Event set telegraph equipment sparking. In May 2024, one of the strongest storms in two decades pushed auroras as far south as Mexico and drew worldwide attention. Understanding the physics helps utilities and satellite operators prepare. For skywatchers, dark skies away from city lights and a clear view toward the north offer the best chance during strong activity.

Myth: the aurora is sunlight reflecting off polar ice. Reality: it is light generated in the atmosphere itself, by gas atoms energized through collisions with solar particles, not reflected sunlight. Myth: the northern lights make a crackling sound. Reality: they occur far too high, around 100 kilometers up, for sound to reach the ground, and the rare low noises some observers report remain scientifically debated. Myth: you can only see auroras at the North Pole. Reality: they form in ovals around both magnetic poles and, during strong storms, reach mid-latitudes. Myth: auroras are always green. Reality: color depends on the gas and altitude, ranging through red, blue, and purple. Myth: they appear only in winter. Reality: they occur year-round, but long, dark winter nights simply make them easier to spot.