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Aurora Borealis: when and where to see them

Northern lights in a starry sky.
Photo: Shutterstock
Northern lights in a starry sky.

What is an aurora borealis?

The Northern Lights and their southern hemisphere counterparts, the Southern Lights, are a fascinating phenomenon. Also known as the aurora borealis, aurora australis, or polar auroras when considered globally, they occur when electrically charged particles from the Sun, particularly electrons, hit the Earth’s magnetic field. These particles are guided by field lines to our planet’s polar regions (the Magnetic North Pole is found in the Canadian Arctic islands). In the upper atmosphere (between 100 and 400 kilometres), the electrons strike atoms of rarefied gases (oxygen and nitrogen), which emit light at specific wavelengths, or colours.

Basically, the atmosphere then acts as a gigantic neon sign. Auroras are usually greenish, although our eyes can’t detect the colour if the aurora isn’t intense enough. They turn red when the eruption spawning them is particularly intense and the electrons carry more energy.

Where should we go to see an aurora borealis?

Polar regions are ideal locations to observe this phenomenon given that the frequency of polar auroras increases at higher latitudes, north or south.

The auroral oval is a region that circles each magnetic pole, and where auroras occur almost daily, at least at weak intensity. In North America, it runs across Alaska, Yukon, Nunavut, the Northwest Territories, the areas bordering James Bay and Hudson Bay (Northern Ontario; Abitibi and Eeyou Istchee Baie-James in Québec), the North Shore, and Newfoundland-and-Labrador.

Auroras are fairly frequent, but often near the northern horizon, in the Québec City area. The difference in latitude with Montreal considerably improves your chances of seeing one there.

Northern lights visible in southern Quebec

Still, when auroras are very strong (following a powerful solar eruption, for example), they may be visible much farther south because the auroral oval expands to cover lower latitudes. On rare occasions, it may extend to the southern United States. In southern Québec, therefore, visible auroras aren’t that uncommon, provided the weather co-operates. To see them at their finest, it’s best to be outside the city.

Auroras are more often visible toward the northern horizon, so if you leave the city, head north to keep the city’s light pollution behind you.

When can we see an aurora borealis?

It’s unfortunately impossible to predict the imminence (and intensity) of an aurora borealis more than 48 to 72 hours in advance. Auroras depend on solar activity. When very large sunspots are visible, violent eruptions can occur.

The particles emitted during solar eruptions can trigger geomagnetic storms on Earth. An aurora borealis is a visible sign of such a storm. Yet even at the peak of the 11-year cycle of solar activity, there’s no guarantee you’ll see an aurora borealis. Several days and even entire weeks can go by without auroras occurring more intensely.

The planetary K-Index, which measures the earth's geomagnetic activity, is a good indicator of the possibility to observe auroras. When it exceeds level 6 or 7, we can expect to see them from southern Québec.

Consult these sites to track solar and geomagnetic activity:

The Space Weather Forecast Canada website provides information on space weather conditions and their potential impact on human activities (satellites, electrical and communication networks, etc.).

To be informed of the high probability of visible auroras, consult daily. The site gives forecasts for the short and mid-term (two to three days) based on what’s happening on the Sun. Also featured are superb photo galleries that many amateur astronomers from Quebec contribute to regularly.

The Space Weather Prediction Center site provides real-time information on solar eruptions (which can cause auroras) and on geomagnetic activity. When the bars in the last graph (at the very bottom of the page) are red and approach the maximum scale value, auroras may be visible even in the city, provided the sky is clear enough.

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