There has been a flurry of activity on the sun over the past few days, which means we may have a chance to see a good display of the Northern Lights tonight.
On Wednesday, the sun erupted in a wave of charged particles that, if they reach Earth and interact with our magnetic field, could put on a spectacular light show.
Our sun goes through an 11-year cycle in which activity waxes and wanes. We are currently in a period of increased activity when the sun produces more sunspots, relatively cooler areas on the solar surface.
But because the sun, which has an incredibly powerful magnetic field, is not a solid mass and different parts rotate at different speeds, the magnetic fields around these sunspots can sometimes become entangled and then spontaneously break, causing a solar flare. These eruptions can disrupt radio transmissions here on Earth.
This image shows several sunspots on the surface of the sun on Friday. The numbers denote the groups traced by space-time scientists. (Spaceweather.com/NASA)
Often these solar flares are followed by something called a coronal mass ejection (CME), in which charged particles erupt rapidly and are carried by the solar wind.
If Earth is in its path, the particles can disrupt our magnetic field, pushing it back until it snaps and the particles head toward the poles.
But not every CME results in spectacular displays of the northern lights, also called the aurora borealis.
For example, there is something called an auroral oval around the north and south poles. How far south the auroras can be seen depends on several factors, including the speed and strength of the particles, and whether or not the oval tilts south (for those in the northern hemisphere).
How and when
According to the US National Oceanic and Atmospheric Administration (NOAA) Center for Space Weather Predictiona moderate geomagnetic storm is possible Friday night.
This chart shows the geomagnetic forecast for July 22 to July 24. (Chris Ratzlaff)
There is some debate as to whether we will get a storm strong enough to be seen at lower latitudes, such as parts of southern Ontario and the northern United States.
Geomagnetic activity is measured by something called the Kp index. The higher the number, the greater the chance of the aurora being visible at lower latitudes. Some aurora watchers predict a Kp index of 8 or 9 — which is pretty high — while others think it won’t be that powerful.
This is because the solar flare associated with the CME was moderate and not that strong.
I agree. NASA & NOAA Forecasts https://t.co/co9I52zA9Z
—@TamithaSkov
Either way, if the skies are clear tonight, you should still be on the lookout.
The best way to see them is to head to a dark-sky spot with a decent view to the north. The sun doesn’t set until late in the evening, so you may have to wait until it’s completely dark.
To see them from a light polluted city like Toronto or Montreal, however, the Kp index would have to be quite strong, like 9 or 10, which is not impossible.
Sometimes, if the storm is weak, the auroras are simply not visible to the human eye. However, since cameras can leave their shutters open for longer exposures, you might try putting the camera on a tripod and taking a 10 to 20 second exposure set to ISO 800 to see if they are there, but just not visible to you.
For updates, there are many free apps like Northern Light Aurora Forecast and My Aurora Forecast & Alerts where you can track the Kp index in real time.
You can also visit websites like Spaceweather.com and SpaceWeatherLive.
And if the forecast doesn’t come true, don’t worry: the sun has just started its maximum phase, so there’s likely to be a few more years of increased solar activity and aurora displays.
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