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What Are the Northern Lights? The Science, Colors and Where to See Them
The northern lights, or aurora borealis, are natural displays of light in the night sky, seen most often near the Arctic. They appear when charged particles from the Sun reach Earth, are guided toward the poles by our planet's magnetic field, and collide with oxygen and nitrogen high in the atmosphere. Those collisions make the gases glow, mostly green, sometimes red, pink or purple.
Here is how the aurora works, why it has different colors and shapes, and where and when you can see it for yourself.
What Causes the Northern Lights?
The aurora is the last step of a journey that starts on the Sun:
- The solar wind. The Sun constantly sends out a stream of electrically charged particles from its outer atmosphere, the corona. This solar wind travels about 150 million km across space and reaches Earth within a few days.
- Earth's magnetic shield. Our planet is wrapped in a magnetic field, the magnetosphere. On the night side, the solar wind stretches it into a long tail, where energy builds up.
- The release. When that stored energy is suddenly released, electrons are accelerated down along the magnetic field lines toward the polar regions.
- The glow. The electrons collide with oxygen and nitrogen atoms and molecules in the upper atmosphere. The gases absorb the energy and give it off again as light, much like a neon sign. According to NOAA's Space Weather Prediction Center, the aurora typically forms 80 to 500 km above Earth's surface.
The same process creates the southern lights, or aurora australis, around the South Pole. The northern lights are simply far easier to visit, because the Arctic is home to towns, roads and airports.
Why Are the Northern Lights Seen Near the Arctic?
Earth's magnetic field funnels the particles into two rings around the magnetic poles, called the auroral ovals. The northern oval lies at roughly 60–75° north and passes over Iceland, northern Norway, Swedish and Finnish Lapland, Alaska and northern Canada. According to NOAA, people living at these latitudes can see the aurora on more than half of the nights in a year, as long as it is dark and clear.
During strong geomagnetic storms, the ovals expand toward the equator, and the lights can be seen much farther south than usual. In the far north, however, you do not need a storm: even low activity can light up the sky. That is why Lapland and Tromsø are among the best places in the world to see the northern lights.
Northern Lights Colors Explained
The color of the aurora depends on which gas is glowing and at what height:
- Green: the most common color, from oxygen at about 100–150 km. Our eyes are also most sensitive to green.
- Red: also from oxygen, but higher up, above about 150 km. It is rarer and usually appears at the top of tall displays or during strong storms.
- Pink, purple and blue: from nitrogen. The lilac-pink lower edge of a bright curtain is a sign of a very active display.
- Yellow and other shades: mixes of the colors above.
Why do photos look more colorful? In the dark, the human eye sees color poorly, so a faint aurora can look like a gray, glowing cloud. A camera collects light for several seconds and shows the green clearly. If you are unsure whether you are looking at an aurora, take a quick photo of the northern sky.
Our founder Moonika saw this firsthand in Rovaniemi: a family standing next to her could not tell the faint green arc above them was the aurora, and their older phones could not capture it. She showed them her photos, took pictures of them under the lights and emailed them over. Without the camera, they would never have known they had seen the northern lights.
What Shapes Can the Northern Lights Take?
- Arcs: a calm, glowing band stretching from horizon to horizon, often the first thing you see in the evening.
- Bands and curtains: the arc breaks into ribbons and tall rays that ripple like curtains in the wind.
- Corona: when the rays seem to meet directly overhead, like a crown or a burst of light. It is the most dramatic form.
- Diffuse and pulsating aurora: soft patches that can blink on and off, often late at night.
Displays often peak around midnight, when the arcs start to twist and move fast. This sudden brightening is called an auroral substorm. It can last a few minutes or, on a good night, a few hours.
Kp Index, Solar Storms and the Solar Cycle
Aurora forecasts are built on a few measures of space weather:
- Kp index: a scale from 0 to 9 that sums up geomagnetic activity worldwide. The higher the number, the brighter and more widespread the aurora. Under the auroral oval in Lapland and Northern Norway, even Kp 1–3 can be enough.
- Solar storms: eruptions on the Sun called coronal mass ejections send extra-dense clouds of particles toward Earth and cause the strongest displays.
- The solar cycle: the Sun's activity rises and falls over a cycle of roughly 11 years. Big storms are most common around solar maximum and in the years right after it.
- The equinoxes: bright displays tend to be more frequent around late September and late March, a pattern known as the equinox effect.
Even the best forecast cannot see clouds. For travelers, the weather forecast matters as much as the aurora forecast.
When and Where Can You See the Northern Lights?
The aurora happens all year round, but you can only see it when the sky is dark. In the Arctic, the midnight sun keeps the summer sky bright, so the northern lights season runs from late August to early April. The best months are often September–October and February–March, and the best hours are usually between 9 pm and 1 am.
To see them, you need three things: a place under the auroral oval, a dark sky away from city lights, and a clear sky. That is why we recommend at least three to four nights in the aurora zone. Read our guides to the northern lights in Rovaniemi and the northern lights in Tromsø, or compare our northern lights tours in Finland, Norway and Sweden.
Northern Lights Myths and Legends
Long before science explained the aurora, people in the North told stories about it. In Finland, the northern lights are called revontulet, or "fox fires," after a legend of an Arctic fox sweeping its tail across the snow and sending sparks into the sky. In the Sámi language, one name for the lights, guovssahas, has been described as "the light you can hear." Many Sámi traditions treated the aurora with respect and warned against waving or whistling at it.
The scientific name has Roman and Greek roots: Aurora was the goddess of dawn, and Boreas the north wind.
Northern Lights FAQ
Yes. Aurora borealis is the scientific name for the northern lights. Their southern counterpart is the aurora australis, or southern lights.
No, not to people watching from the ground. The aurora happens far above us. Very strong geomagnetic storms can, however, disturb power grids, satellites, radio and GPS signals.
Usually not. Some people report faint crackling during strong displays, and researchers in Finland have recorded crackling sounds during auroras, but most nights the show is completely silent.
Not every night, but often. Under the auroral oval, the aurora appears on more than half of dark nights. Whether you see it depends mostly on clouds and darkness.
Yes, if the display is bright. A full moon can wash out faint auroras, so the days around the new moon are best for weak activity.
Yes. Auroras have been observed on Jupiter, Saturn and other planets with a magnetic field and an atmosphere.
See the Northern Lights for Yourself
Reading about the aurora is one thing; standing under it is another. Our local guides follow the forecasts every evening and take you to the clearest skies. Choose the Finland Northern Lights Tour, the Tromsø Northern Lights Tour or the Lapland Northern Lights Getaway, or see all our northern lights tours.
