Get ready for some amazing displays of the Aurora Borealis Friday night

Solar flares are ranked on a two-part scale: a letter (A, B, C, M, X) for its class and a number (1-9) for its strength within that class. A & B flares happen all the time and are the barely noticeably. C-class are common, weak ones that have little to no effect here. M-class flares are moderate ones that can result in minor and brief radio blackouts, and they can throw off weak CMEs that can result in minor geomagnetic storms here at Earth (thus slight increases in auroral activity). X-class are the most powerful flares. The high-energy x-rays blasted out by these can cause widespread radio blackouts and can interfere with satellites and spacecraft. They can throw out immense, fast-moving CMEs that can trigger intense geomagnetic storms and bright, widespread auroral displays. Each letter of the scale represents flares that are ten times more powerful than the flares of the letter class below (X1 is ten times stronger than M1, etc), with the numbers filling in the gaps between. For example: an X2-class flare is twice as strong as X1, and 20 times stronger than M1.

The Power of the Sun

One special feature of the X category is that it's open-ended - it can go higher than X9.9. The first and most powerful solar flare ever witnessed - the Carrington Super Flare from September 1859 - has no official ranking, because we didn't have the satellites and recorders in place at the time to measure it properly. So far, estimates made from eyewitness accounts of the auroras it produced put it as an X45-class flare. The only single flare that has come close since then happened on November 4, 2003. The flare was so powerful that it actually saturated the satellite instruments, causing them to cut out at around the X17 mark, but based on how the flare was ramping up before that, scientists estimated it as X28-class. Later, based on watching the effects the flare had on Earth's ionosphere, that estimate was pushed even higher, up to X45! Another event, actually the combination of three different M-class flares in June of 2012, didn't match the intense flash of these X-class flares, but the combined effects of their CMEs was found to be just as powerful as the CME from the Carrington Super Flare. Given that the geomagnetic storm kicked off by that flare back in 1859 fried telegraph wires and electrocuted operators, such a storm hitting Earth now has the potential to damage satellites and cause widespread blackouts. A study done about this estimated that it would cost the world economy trillions, and it might take months to completely restore power grids and infrastructure back to normal.

Nothing to worry about

With Wednesday's flare, ranking 'only' at X1.6-class (so one of the weakest of the X-class), it won't cause anything close to these extreme events. We're still going to feel the effects of it, though. 

The coronal mass ejection from the flare was Earth-directed, and is expected to sweep past our planet sometime late Friday. We're in no danger here on the ground from this, though, since the Earth's magnetosphere will deflect most, if not all of the solar particles around the planet. However, as that happens, the magnetosphere can become compressed, squeezed by the combined magnetic fields of all those particles, and this can funnel some of those high-energy particles down towards the poles. Once they enter the atmosphere, these particles interact with the molecules in the air - oxygen and nitrogen - causing them to fluoresce. Depending on the depth of the atmosphere these particles penetrate to, you get different colours. At the tallest heights (above 200 kms) we usually see red, as the particles interact with oxygen. At mid-range heights (100-200 kms), it's typically a mix of blues (from nitrogen) and greens (from oxygen). At lower heights (below 100 kms) it's usually more purples and violets (from nitrogen).

The U.S. National Oceanic and Atmospheric Association's Space Weather Prediction Center produces a forecast of auroral activity, called OVATION, which can be accessed on their website (click here). Due to the slight unpredictability of these events (and the experimental nature of the forecast), they only prognosticate about a half-hour ahead, so check back often. The view from last Thursday night, when there was a minor (G1) geomagnetic storm happening from an earlier CME, looked like this:

Credit: NOAA

Focusing on North America, a moderate (G2) storm is expected during the day Friday, which should ramp up to strong (G3) into Friday night. That should produce an even more intense band of auroras, which will likely spread much further south than what's shown in the above image. The best time for viewing will be between 11 p.m. and 2 a.m., for whatever local time zone you observe, but given how unpredictable auroras are, anytime between Sun-down and Sun-up might be good. Natural Resources Canada has their own space weather forecast page (click here), and NOAA's website is a valuable resource as well (click here).

If you head out to view what should be a spectacular event, check the cloud conditions in your area (here on our website or on cleardarksky.com) and get as far away from light pollution as possible. Head outside of any urban areas, with your best bet being to aim yourself north. Also, if you manage to capture any images or video of these, we'd love to see them and feature them on our website. You can upload them by accessing the video or photo gallery on the front page of our website (click here).