The Northern Lights—also known as the Aurora Borealis—is a natural phenomenon that illuminates the night sky in northern regions of the Earth throughout the year. However, when it comes to seeing this brilliant light display for yourself, you'll have to visit a dimly-lit destination in the auroral zone, where the Northern Lights are likely to occur, preferably during the darker seasons from September to April.
The weather conditions on the sun and earth determine whether or not the aurora can be seen, as do the light pollution levels of where you're viewing it. When visible, though, the Northern Lights can be seen up to 260 miles (400 kilometers) away on the horizon due to the curvature of the earth.
What Causes the Northern Lights
The aurora is caused by large numbers of electrons originating from the sun colliding with air particles along Earth's magnetic field. The air then lights up in a similar manner to what happens in a fluorescent light tube, around 60 miles (100 kilometers) above the earth's surface. The resulting colors of the Northern Lights are caused by these reactions reflecting onto the gases in Earth's atmosphere. It is most common to see green lights, though a reddish glow that appears like a dark sunrise is also sometimes visible, specifically in Scandinavia.
Best Places to See the Aurora Borealis
While you might be able to see the Northern Lights from anywhere in the auroral zone, the aurora is almost always visible from locations beyond the Arctic Circle, which lies near the towns of Rovaniemi, Finland, and Bodø, Norway. The Northern Lights can be viewed from other northern locations as well, but the northern half of Norway and Sweden, as well as all of Iceland, are famous for having "the best seats" for viewing the Aurora Borealis.
The best places to see the Northern Lights any time of year are the Norwegian counties of Tromsø, Norway, and Reykjavik, Iceland, which offer great views of the lights even at the minimal level of auroral activity. Out of all Nordic destinations, Tromsø and Reykjavik provide the longest and darkest viewing season since they are located beyond the Arctic Circle, especially during polar nights when there is no sunlight.
If you don't want to go that far north, the next-best location to see the northern lights is the region between the Finnish town Rovaniemi and the Norwegian town Bodø, just along the edge of the arctic circle. Additionally, locations as far south as Umeå, Sweden, and Trondheim, Norway, may not be as reliable for views of the lights, but they offer a good alternative for the average traveler. These places require only slightly stronger geomagnetic activity to enjoy the natural phenomenon up close, so you won't see them as often.
Best Time to See the Aurora Borealis
Although the Northern Lights are constantly happening above the Earth on some level, it may be harder to see them from the ground at different times of the year. As a result, the best times to see the lights are when it's dark out longer.
Places above the Arctic Circle, which get less light year-round, typically experience the best viewing season any time between September and late April. The further south in Scandinavia you go, the shorter the Aurora Borealis season will be, meaning you'll likely only see the Northern Lights between mid-October and March in that region.
The optimal time of night for the northern lights is 11 p.m. to 2 a.m. Keep in mind that most visitors head out to begin their watch around 10 p.m. and conclude their night around 4 a.m. since the northern lights can be hard to predict (just like the weather in Scandinavia). If you do not see the northern lights as expected—even if the timing is right—locals recommend to simply wait for one to two hours; nature tends to reward the most patient.
Predicting Visibility of the Northern Lights
How often the Northern Lights are visible depends on where you are trying to see them. In locations nearer the Arctic Circle, like Tromsø and at the North Cape (Nordkapp) of Norway, you can see the Northern Lights every other clear night, if not even more frequently. On the other hand, you may only see them two or three times a month in more southern locations like central and southern Sweden.
To forecast the northern lights, you need to know the location where you will be watching them and the expected geomagnetic activity on the night of your trip, which is measured by a Kp index from 1 to 10. The higher the Kp value in the forecast is, the farther south the northern lights will be visible.
Check your travel dates in the official NOAA Space Weather Outlook, which predicts geomagnetic activity for the next 27 days year-round, then get the Kp number listed there. Once you've determined the Kp number, check to see if the Northern Lights will be visible from your location:
- Northern lights predictions for locations like Tromsø and Reykjavik show the northern lights on the horizon even at 0 Kp from autumn to spring. At least 1 to 2 Kp (and higher) will guarantee that the northern lights are directly overhead at these locations.
- Rovaniemi, Finland, also only needs a Kp index of 1 for visibility of the northern lights on the northern horizon.
- As far south as Umeå and Trondheim need at least 2 Kp to predict seeing the lights on the horizon, or a Kp value of 4 to enjoy them overhead.
- Down in areas around the Scandinavian capitals Oslo, Stockholm, and Helsinki, the Kp index has to be at least 4 for northern lights visibility on the northern horizon or 6 for the northern lights to take place directly overhead.
- In comparison, central Europe requires 8 to 9 Kp (very high auroral activity) to see the northern lights at all.
However, while activity is forecast year-round, the northern lights generally cannot be seen May through September. The visibility of the northern lights also depends on local weather conditions as cloud cover will hide the northern lights even if the prediction points to a likely occurrence.