Northern Lights may shine across parts of Canada tonight
Solar storms are expected to sweep past Earth, which may spark bright aurora displays across some parts of Canada.
Eyes to the northern sky overnight on Tuesday, for a chance to spot the Aurora Borealis dancing overhead.
Early on Sunday, April 13, the Sun released two massive eruptions into space, one right after the other, with both headed almost directly towards Earth.
Three views of the April 13 2025 solar eruptions, as they expand over a period of two hours into a 'halo CME' on its way towards Earth. The yellow arrows arrayed around each capture show the outer edge of the cloud (at the inner edge of the arrows), and the direction the cloud is travelling. (NASA/ESA SOHO, Scott Sutherland)
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According to space weather forecasters, the 'one-two' punch of these coronal mass ejections sweeping past us tonight is expected to result in a G1 (minor) geomagnetic storm in the hours after midnight EDT.
This could be followed up by a G2 (moderate) storm a few hours after, as the second solar storm arrives and adds its impacts on Earth's geomagnetic field to those from the first.
Additionally, SWPC has issued a G3 (strong) geomagnetic storm watch for overnight tonight, due to the potential for activity to ramp up even further.
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Due to the timing of these two events, any auroras that spark across the eastern half of Canada will likely be confined to northern regions of Atlantic Canada, Quebec, and Ontario.
The G1 and G2 storms, as well as the potential G3 storm, all favour the western half of the country, though. Auroras may start out across the central and northern Prairie provinces, but could push down across the southern Prairies in the hours before sunrise.
Will we see the auroras?
Whether the auroras occur as forecast will need to wait until the solar storms reach the satellites positioned at Lagrange Point 1, 1.5 million kilometres out from Earth. Instruments on those satellites will then be able to tell us the exact conditions in the CME clouds, and thus give us an indication of what kind of impact they'll have when they reach us, a short time later.
The above map, based on data from NOAA's Space Weather Prediction Center, shows the likely extent of Northern Lights throughout the night on April 15-16, based on the expected impacts of the CMEs. The lighter yellow colour indicates the maximum possible extent based on a G3 geomagnetic storm, with the auroras visible along the northern horizon for areas along the southern edge. The orange represents the greater potential for seeing the auroras directly overhead.
For those of us here on Earth, whether we see any auroras that do occur depends on the sky conditions overnight from Tuesday to Wednesday.
In the eastern half of Canada, skies will be mostly cloudy to overcast. Northern Ontario is expected to see clear skies tonight, however, as well as across central Alberta and most of British Columbia.
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What's going on?
The solar storms headed towards Earth are the result of two large 'filaments' on the surface of the Sun.
Due to the Sun's magnetic fields, massive arcs of solar plasma can stretch for immense distances across its surface. When these arcs are seen along the edge of the Sun, they are called prominences. When they are viewed against the brighter surface of the Sun, though, they are known as dark filaments.
Some filaments can have a very tenuous connection to the Sun's surface, and even the smallest disturbance can cause them to tear away and launch into space. That is what happened Sunday morning, as seen below via NASA's Solar Dynamics Observatory.
The first filament eruption (top row) shows the filament just before (top left), and the 'canyon of fire' splitting open in the wake of the eruption (top centre and top right), which sends the filament as a CME towards the lower left of the view. The second filament (bottom row) erupts towards the lower right, as another 'canyon of fire' expands away from the eruption point. (NASA SDO/Scott Sutherland)
As the two filaments expanded out into space, one was aimed slightly ahead of Earth, while the other will pass slightly behind. Both are expected to make glancing blows on Earth's geomagnetic field as they sweep by.
The first is expected early on April 16, with the second showing up just after.
The ENLIL model of solar wind density and speed shows the two CMEs arrive at Earth, with the denser portions of each passing to either side of the planet (top left). (NOAA SWPC)
When these two solar storms arrive, they will cause a spike in the amount of solar particles interacting with Earth's magnetic field. As a result, some of those particles will become trapped along the field's lines, and thus will be funnelled down into the upper atmosphere.
Collisions between these high-energy particles with oxygen and nitrogen in the air cause the atoms and molecules to become energized, and they release that excess energy as flashes of coloured light. Each particular atmospheric component emits a different colour of light — atomic oxygen emits red, molecular oxygen emits green, and molecular nitrogen emits blue — with different colours mixing together to produce shades of purple, orange, pink, and even white.