Stargazers across the country may have a chance to see the Aurora Borealis this weekend, following an immense eruption from the surface of the Sun.
Just after midnight, Eastern Daylight Time, on April 22, 2021, an active region on the Sun emitted a weak, C3-class solar flare. Flares like this are relatively common during the Sun's more active periods. With the start of a new solar cycle in December of 2019, we will see more and more of these in the years ahead.
Multiple views of this solar flare, over a period of about 30 minutes, taken by NASA's orbiting Solar Dynamics Observatory (SDO). Credit: NASA/SDO/Scott Sutherland
Flares of this magnitude tend to have minimal impact on Earth (M-class and X-class are the ones to watch out for). However, in the hours after the flare, the NASA-ESA Solar and Heliospheric Observatory (SOHO) captured very faint indications that this event had resulted in a coronal mass ejection.
During a solar flare, loops of magnetized solar plasma untangle and reorganize themselves. This process can cause some of the plasma contained along these loops to be launched out into space by the flare's energy. These clouds of plasma are called coronal mass ejections, or CMEs.
This view of the region of space surrounding the Sun, taken by SOHO roughly 7 hours after the solar flare, shows an expanding 'halo' of plasma in a coronal mass ejection. As this halo is very faint in the original images, it has been enhanced to make it easier to see. The planets Mercury and Venus can be seen in this view. The Sun is located behind the dark circle in the centre of the image (indicated by the white ring). Credit: NASA/ESA/Scott Sutherland
After analyzing the images of this CME, forecasters with NOAA's Space Weather Prediction Center determined that at least part of this cloud was on a trajectory towards Earth. As a result, they have issued a G2 geomagnetic storm watch for Sunday, April 25.
"The forecast now calls for likely geomagnetic storm conditions, with the potential to reach G2 (Moderate) storm levels, therefore, a G2 geomagnetic storm watch has been issued for 25 April," they wrote on Friday. "While forecast confidence in an Earth-directed component is fair, timing and intensity confidence is lower. Continue to follow our webpage for the latest information."
This map plots the likely extent of auroras at different levels of geomagnetic storm strength. For a G2 geomagnetic storm, the southerly extent can be seen between the green and yellow curves.
WHAT IS GOING ON HERE?
Solar flares, coronal mass ejections, and geomagnetic storms are different parts of what we call space weather.
This artist impression shows the various aspects of space weather, including the last 400 years of the Sun's 11-year solar cycles, all in one graphic. Credit: NASA
Solar flares are explosions of energy from the surface of the Sun. Look at a sunspot with the right camera filter (as shown in the images from the Solar Dynamics Observatory above), and you will see they are surrounded by bright 'coronal loops'. These loops appear this bright because they have tons and tons of magnetized solar matter swirling around them. The more chaotic and jumbled up these loops are, the more likely they are to suddenly and violently unravel and form new, simpler connections. When this happens, a significant amount of energy can be released, and this is what we call a solar flare. While most flares are weak, such as the A, B and C-class, we begin to take notice when we see M-class and especially the incredibly powerful X-class flares.
A geomagnetic storm occurs when Earth's geomagnetic field — which is generated by the molten metal in the planet's core — experience some kind of disturbance. This usually happens due to changes in the constant flow of particles streaming away from the Sun, which we call the solar wind. Occasionally (and more frequently towards the 'peak' of a solar cycle), we see these disturbances due to coronal mass ejections sweeping past us. The disruption causes Earth's magnetic field to fluctuate, and some of the solar particles passing by us become caught in the field and are drawn down into Earth's atmosphere.
Since these particles carry a significant amount of energy with them, when they collide with atoms and molecules of oxygen and nitrogen in our atmosphere, they transfer some of that energy in the process. The atoms and molecules then dump that energy, emitting it as flashes of coloured light. These flashes are what we see during displays of the Aurora Borealis and Aurora Australis, aka the Northern and Southern Lights.
Different types and colour combinations of auroras are shown here. Reds and greens are emitted by oxygen, while blues and pinks are produced by nitrogen. Arcs and pillars (Tobias Bjørkli/PIXELS), Bands and rays (GETTY), Corona (CBC), Rays and Pillars (AuroraMax/CSA), Patches and STEVE (Team Tanner)
Aurora displays are harmless wonders to behold, occurring between 100-400 km above our heads. Still, space weather does have its dangers.
Intense solar flares bombard the planet's upper atmosphere with x-rays, resulting in prolonged radio blackouts. Astronauts on board the International Space Station take shelter in shielded spacecraft until such a flare subsides. Also, orbiting satellites and spacecraft can suffer electrical problems during geomagnetic storms. Exceptionally strong geomagnetic storms can even cause electrical blackouts on the ground.
This artist's rendition shows the extent of the 1989 Quebec Blackout, which was caused by an intense geomagnetic storm. Credit: NASA
No danger is expected from this weekend's space weather events. The solar flare from April 22 was relatively weak, and the resulting coronal mass ejection is fairly diffuse. This could produce some impressive auroral displays, however. If the timing works out as expected, auroras are more likely on Sunday night. If this CME arrives earlier than expected, though, Saturday night would be the time to watch.
Stay tuned for more updates.