What Creates the Colours in Northern Lights?
Get ready—scientists predict 2025 will be a prime year for aurora borealis displays.
Find yourself a dark spot away from city lights to view this celestial ballet of green, red and violet that emerge like ribbons racing across the sky.
But as soothing as they seem, the colourful lights are actually born in an act of chaos.
Explosive plasma storms erupting on the sun send clouds containing billions of charged particles hurtling through space. Carried by what’s known as a solar wind, these particles reach Earth in a couple of days and slam into our upper atmosphere at incredible speeds of up to 750 km per second.
Although most of these solar particles are deflected away, a certain amount ride Earth’s magnetic field to the poles where the protective field is at its weakest, and they sneak through into our atmosphere.
When they enter, these particles collide with gases, creating a flash of light as the electrons shift rapidly between orbits of differing energy.
“It’s similar physics to what happens in neon signs. Electricity excites the atoms in the gas within the glass tubes. That’s why these signs give off their brilliant colors,” says Danielle Pahud, an instructor in the Physics and Astronomy Department at the University of Manitoba.
The colours generated in an aurora are a product of the type of gas involved and how high in the atmosphere these collisions occur.
Green is the most common shade, created when charged particles carried by the solar wind collide with oxygen molecules at altitudes of 100 to 300 km. Higher up—at around 300 to 400 km—collisions with oxygen atoms produce red. Excited nitrogen atoms produce the most prized of auroral colors: lilac-pink, which you see in super active displays, where particles are penetrating down to roughly 100 km above ground. The lower edge of an aurora will sometimes display a pink or dark red fringe, which is emitted by nitrogen molecules at altitudes of around 100 km.
The more violent the plasma storms are on the sun, the better the chances we have of seeing spectacular light shows above Earth. The current astral timetable is tilted in our favour.
“The sun has an 11-year solar cycle. Solar maximum has just been declared, so we are now at the peak. In the middle part of this cycle, the sun releases the most coronal mass ejections. These are the storms that if propelled towards Earth will tend to generate the most incidence of the northern lights,” says Pahud.
Keep your eye to the sky — more dazzling facts
The best place to see aurora borealis: any destination in the “auroral zone,” which is the area within a 2,500-kilometre radius of the North Pole. This includes Churchill, Man., with an average of 300-plus nights of aurora activity annually.
Prime time of year for viewing: between September and April, when the sky gets darker. March is generally considered best in North America, with more geomagnetically active days than any other month. October is a close second.
Why northern lights look less vivid in real life than in photos: the human eye is not good at detecting colour at night. The brightest auroras are roughly comparable to moonlight. Cameras are far more sensitive to this low light, and their long exposures can capture colours and details we don’t see.
Northern lights can be seen from above, too. Astronauts on the International Space Station get an entirely different perspective. The auroras typically range from 100 to 300 km above Earth’s surface, while the space station orbits at an altitude of 400 km.
These light shows happen on other planets. The auroras on Jupiter are said to be particularly striking—hundreds of times larger and more intense than on Earth because of the gas giant’s powerful magnetic field.
Northern lights can be accompanied by audible noises, if conditions are right. Historically, the idea that auroras produce sound has often been dismissed as a psychoacoustic phenomenon, but researchers at Aalto University in Finland recently recorded popping and crackling sounds. They say these sounds may come from a layer of warm air about 80 metres above the ground, which can occur on calm, cold winter nights. This layer allows a type of static electricity to accumulate in the sky during a geomagnetic storm. When that electricity is discharged, it can be heard from the ground.
The northern lights also happen to be part of the University of Manitoba’s brand story, celebrating the colourful collisions of people and ideas that move our province and world forward.