What Causes the Northern Lights to Shine?

An expert explains.

The story of the Northern Lights (or Aurora Borealis) starts deep inside the Sun. The core of the Sun is a nuclear furnace that converts hydrogen atoms into helium atoms through nuclear fusion. This is a process that releases a tremendous amount of energy. When you look at the Sun, essentially what you see is a huge hydrogen bomb that is contained by the force of gravity. It has been around for over 4 billion years, and about that much more time is left before the core runs out of hydrogen. All the energy that is generated in the core moves out through the Sun as electromagnetic radiation, or light.

The sun's electromagnetic radiation (or light). Photo courtesy of Nasa.

You can imagine that if you were close to the surface of the Sun, the amount of energy hitting you would be tremendous. You could not survive there. Similarly the atoms in the solar atmosphere can't get away unscathed either. Some of their electrons are stripped from them by the Sun's energy, making them positively charged ions. This plasma (a gas of charged particles) is so hot it continuously expands outward through space creating a solar wind.

A solar wind, hitting Earth's magnetosphere. Photo courtesy of Nasa. 

These solar wind particles carry a lot of energy, and eventually stream past the Earth's own magnetic field, the magnetosphere. It is a huge windsock-shaped magnetic bubble, and acts as a partial shield against the solar wind. The magnetosphere also contains plasma, the origin of which is not well understood yet. The interaction of the solar wind and the magnetosphere drives huge electric currents in the magnetosphere. Because of these currents, the electrons and protons in the plasma come down in field lines.

An example of the electric current 'field lines'. 

The gas in the Earth's upper atmosphere becomes excited and ionized as it absorbs the incoming energy. The atoms in our atmosphere re-emit this energy in the form of light – the aurora. Exactly the same way we make a neon sign glow by sending a current through it! The aurora mostly originates from a layer in the atmosphere about 80 km to 300 km above us. We see it in "sheets," sometimes changing quite rapidly due to the shape and dynamics of the Earth's magnetic field that guides the particles.

The flow of particles coming towards the Earth is usually roughly ring-shaped, centered around the magnetic poles of the Earth. In Ontario's far north, for example Moosonee and Polar Bear Provincial Park, you can see the northern lights on many clear nights. Even further north, for example in Yellowknife in the NWT, northern lights are actually visible every night! In places like Sudbury we usually have to wait for strong solar wind activity – a solar storm, which makes the ring of aurora around the north pole expand southward, to see the lights.


To learn more about increasing your chances of viewing the northern lights, visit this recent article: Increase Your Odds: Viewing the Northern Lights. And, to view the northern lights from the comfort of home, you can check out the AuroraMAX camera by the Canadian Space Agency. 

The colour of the aurora depends on what gas is excited or ionized and at what altitude this happens. At the highest altitudes oxygen atoms emit red light. At lower altitudes green light from oxygen atoms starts to dominate. When solar activity is very high, we may also see blue and purple light coming from the lowest part of an auroral display. Nitrogen molecules emit these colours.

So when you are lucky enough to see the spectacular display of the aurora, what you are really witnessing is the interplay between the Earth and the Sun's magnetic fields and the energetic particles flowing through them. You are witness to the beauty of some very complex physical processes. The beauty of physics!

About Simon McMillan

Simon is an astonomer, and staff scientist, at Space Place in Science North, Sudbury, ON. There, he oversees space programs and exhibits. He is passionate about our beautiful universe, and would be happy to answer any of your questions.

Recommended Articles

Join the Ice Fishing Village on Lake Nipissing

A complete guide to huts & bungalows you can rent around North Bay and Callander Bay.

Fish for one of the World's Rarest Species of Trout

Found only in 12 remote Ontario lakes–and nowhere else in the world–the aurora trout is a special fish.

Spectres of the Past: A Ghost Town Field Trip

Follow this trail of abandoned communities on a road trip through the history of Northeastern Ontario

Complete Guide to Moosonee & Moose Factory Island

12 essential experiences for visitors.

Northern Lights in Northeastern Ontario

Where to see Northern Lights In Canada: Northeas5 Great Spots in The Seven to Find the Aurora Borealis tern Ontario

Ontario's Secret Lagoon

Discover paradise just outside of Sudbury

The Northern Lights Trip Planner

3 trip ideas for an illuminating experience in Ontario

Best Things to Do in Kirkland Lake: The Town that Gold Built

Check out a self-guided gold mine tour, a northern chateau museum, and get some beach time!

11 Best Things to Do in Kapuskasing, Ontario

Gourmet cheese, hammocks in the park, and Canadian-Szechuan cuisine await in this historic lumber town

A Guide to Mushroom Hunting

How, when and where to go, and what to look for

Moosonee Guide: Moose Factory Island

Gateway to The Arctic Part 4: Across the River to Moose Factory Island

Mountain Lions, Foxes and Bears, Oh My!

Tracking Footprints in Northeastern Ontario

An Insider's Guide to Manitoulin Island

12 communities, sights, hikes and experiences that most first-time visitors miss!

Ice Fishing is All About Making Memories (and Catching World Class Fish!)

Check out the best ice hunt rentals in Northeastern Ontario.

Crossing The Northern divide

You don’t need a passport to hop this border!

These Glamping Geodomes Are Now Available To Book Near Manitoulin

We sat down with owner and operator Brian Still to learn more about his new luxury glamping destination just north of Manitoulin Island.

Northeastern Ontario Snowmobile Rentals, Repairs & Dealers

Whether you're looking to buy, rent, or repair your current ride, here are all the best places to help get you on the trails this season. 

Stompin' Tom sang about it. The fur traders paddled through it. And the town's mayor made it famous.

Visit Voyageur Country and discover the magic for yourself.

This is the Must-Do Road Trip of Summer!

The Georgian Bay Coastal Route winds through some of Northeastern Ontario's most beautiful landscapes.

Manitoulin Island Camping and RVing Guide

Have you explored the world's largest freshwater island yet?