The Northern Lights, or Aurora Borealis, are technically present in the sky year-round, driven by continuous solar activity. However, visibility in May is complicated by the amount of daylight. As the Northern Hemisphere approaches summer, the sun stays above the horizon much longer, drastically reducing the hours of necessary darkness. The natural light of late spring overpowers the faint spectacle, making May one of the most challenging months for aurora viewing.
The Challenge of Astronomical Twilight
The main obstacle to seeing the Northern Lights in May is the lack of true night at high latitudes. For the faint glow of the aurora to be visible, the sky must reach complete darkness, defined by a solar elevation angle.
True darkness is achieved only when the sun is 18 degrees below the horizon, a period known as astronomical twilight. At this point, the residual light from the sun is fully dissipated. In May, popular viewing locations like Iceland or Southern Scandinavia never reach this 18-degree threshold.
Instead, these regions experience civil twilight (sun 6 degrees below) and nautical twilight (sun 12 degrees below), where the sky remains perpetually illuminated with a deep blue glow. This persistent residual sunlight is strong enough to completely wash out the subtle light emissions of a typical aurora display. Consequently, the light show remains invisible because the dark canvas of night is never fully established.
Latitude and the Visibility Threshold
The impossibility of achieving astronomical twilight in mid-range northern locations suggests moving significantly further north. Daylight duration depends heavily on latitude; the closer a location is to the magnetic North Pole, the shorter the twilight period. Locations further south, such as the mainland coast of Norway or Iceland, experience the “Midnight Sun” effect, where the sky is too bright.
Moving to extreme northern latitudes, such as the Svalbard archipelago or northern Greenland, can offer a brief window of potential visibility in early May. These regions are positioned directly beneath the auroral oval, the ring-shaped zone where auroral activity is concentrated.
In these extreme locations, the sun may briefly graze the 12-degree threshold of nautical twilight around midnight in the first weeks of May, allowing for a fleeting period of semi-darkness. This slight increase in darkness, combined with being directly under the most active part of the aurora oval, provides a slim chance for a sighting. A typical aurora visible from this high latitude would be overhead and thus appear brighter than one viewed from the horizon further south.
Overcoming Dim Light with Solar Storms
When facing a twilight sky, the only way to guarantee visibility is for the aurora itself to be exceptionally bright. Auroral intensity is measured using the Kp index, a scale from 0 to 9 that indicates the level of global geomagnetic disturbance. Only a major geomagnetic storm, typically registering as a high Kp value, generates an aurora powerful enough to penetrate the veil of perpetual twilight.
These intense storms are usually triggered by a Coronal Mass Ejection (CME) from the sun, which sends a massive cloud of highly charged particles toward Earth. When this cloud collides with the planet’s magnetic field, it dramatically energizes the atmospheric gases, resulting in a significantly brighter and more active display.
A strong Kp event, perhaps a 7 or higher, produces light emissions brilliant enough to outshine the ambient blue glow of a May sky. The aurora becomes a dynamic, fast-moving curtain of light that extends across a large portion of the sky, not just a faint arc on the horizon. The primary function of such a strong solar storm in May is to inject so much energy into the atmosphere that the resulting light becomes visible despite the sun’s position. Without this level of intense solar activity, the May aurora will remain hidden, even in the most northern locations.