Beauty and The Beast - The Sun’s hand in our colorful night skies.
We’ve pretty much all heard of or, if lucky enough, seen the northern lights that have coloured the night skies of late. To many, what could only be seen on a trip to Iceland was now visible from their own homes; the Aurora Borealis took populations by surprise. How come this isn’t a more common occurrence? Is there something wrong with the Sun, the atmosphere, or our magnetic field? Is this concerning…or cool? Let’s first see how these phenomena occur, after which we can delve into why exactly the night sky outside your window is suddenly green.
What’s been going on with the Sun recently?
Our host star, ruler of our solar system, is currently going through…a phase. It is at the peak of its 11-year activity cycle. The determinant factor of this cycle is the solar magnetic field, which flips, causing the Sun to, well, freak out. As the Sun’s core keeps fusing hot, dense hydrogen, the movement of these charged particles creates a magnetic field. Now, given the unbelievably high mass of the Sun, this magnetic field is, in turn, extremely powerful – 2,500 times stronger than Earth’s. With such power, comes a significant impact on both the solar system and the Sun itself. Around every 11 years, the north and south poles of the giant magnet that is the Sun, switch places. The magnetic field polarity switches due to the turbulent motion of the inner molten, or in this case plasma, core. I don’t really understand how physicists are so casual about that fact…but I digress. When this switch occurs, the charged particles on the surface of the sun are also affected and hence move around, resulting in heightened solar activity. Solar physicists rely on this activity (or lack thereof) to approximate where on the solar cycle the Sun is. Judging by current activity, we’re at the solar maximum – the poles are officially switching.
Solar flares and Sunspots
The activity on the Sun can be detected by Sunspots. No, I am not referring to the ones you get after hours of tanning on the beach. Appearing as relatively small black blobs on the Sun’s surface, they are areas of magnetic flux pushing their way out of the stellar interior. “Flux” is a real jargon-y physics word but it just means a flow of energy or fluids. With this fluctuation in energy, comes a fluctuation in temperature too. The solar surface becomes slightly cooler at some points than its surrounding surface, creating a dark spot indicating these relatively cold regions. Because some areas are cooler, they also shine dimmer, making them look, by comparison, far darker than the bright surface around it.
Magnetic fields operate through magnetic field lines. These span around the magnet going out from the north pole and into the south pole. In a complex, turbulent, massive body like the sun, the magnetic field lines aren’t as contained as we’d like them to be. As a result, there is a chance that these lines cross. When this happens around a Sunspot, an area of higher flux than on the average surface, a Solar flare forms. These are bursts of high energy radiation; UV rays, X-rays, gamma rays, ejecting from where those magnetic field lines meet. At their worst, these flares come with a coronal mass ejection (CME), including charged particles from the suns surface. A Solar storm is when we have the whole concoction – Sunspots, Solar flares, and CMEs. If unlucky enough, Earth becomes a target for these unpredictable storms, especially during a Solar maximum.
The Aurorae
Though solar storms can be dangerous, the Sun still undoubtedly also protects us from detrimental cosmic rays - radiation coming from everything else in space. Despite most of them being deflected by the Sun’s magnetic field, our solar system remains under threat from the intense radiation beaming through the universe. So, Earth not only has its host star’s radiation to worry about, but also that coming from stars and galaxies far, far away.
Thankfully enough, the Earth has got an invisible shield of its own. Our magnetic field, just like the Sun’s, deflects most of the harmful radiation coming from the universe and, most importantly, the Sun. Now, this shield is definitely not fool-proof, but its power is evident when we look at the proof of its might – the Aurorae.
As the molten iron and nickel in Earth’s core turn around, the charged particles inside create a magnetic field around the planet. The two poles of the planet act as the poles of this giant Earth magnet – north is currently in the Arctic, and south is down by Antarctica. Aurora Borealis is the name for what are most commonly known as the northern lights, and Aurora Australis are those seen in the south pole. We hear more of the northern lights though, because more people inhabit the northern hemisphere than the southern hemisphere. As the charged particles from the Sun are redirected to the north and the south poles, they ionize the atoms in the atmosphere, creating magnificent shows of colour. The colours we see depend on the atoms ionized. Most commonly, the Aurorae are observed to be green, as that is the colour of the light emitted by ionized Oxygen. One could also see pink, purple, or even blue coloured aurorae which are attributed to ionized Nitrogen.
How come aurorae are so far south now?
Though the poles do redirect most charged particles, again, they can’t catch them all. That means that if a solar storm is strong enough, radiation can break through and hit our atmosphere.
Our atmosphere serves as a shield of its own as well, as the ionization of the Oxygen and Nitrogen means the capture and re-emission of the high energy particles by these atoms. Even so, that doesn’t mean you should tan sunscreen-free! UV radiation still very much passes through our two-layers of invisible shields.
Satellites in orbit can also be hit by the high energy radiation and particles, possibly malfunctioning as a result. These include GPS satellites, telecommunications satellites, and even space telescopes. The very internet I’m relying on for you to read this, could be damaged as the electrical systems that keep it running can be easily affected by oncoming charged particles. The takeaway from this threat is one – even the Sun wants us off those damn phones.
One more thing...
So, this whole thing is pretty much all about the Sun’s magnetic field flipping. But the Earth has a magnetic field too. So, how come that doesn’t flip?
Well, it does. Scientists agree that our Earth’s polar switch cycle can happen either every tens of thousands of years or it could also take millions of years. As imprecise as that approximation is, we know our poles haven’t flipped in over 700,000 years. My takeaway from that, is that a switch is imminent. Since it shouldn’t be instantaneous, a flip of the poles would mean that we could be left with a weakened or completely gone magnetic field for while – leaving us vulnerable to the Sun’s power. Interestingly, our poles are in motion. The north pole is moving further south at a rate of 55km per year. Mind you, this speed accelerated from just 16km in the last few decades. Personally, I worry about this flip around every 3 months, but as long as it doesn’t flip during this solar maximum, we should be okay-ish.
Conclusion
Space is scary. The Sun is a giant ball of flame with exploding charged particles and high energy radiation. The Earth is a fragile little rock floating through space, but it makes sure to protect itself as much as it can. As teeny tiny humans, we’re rather helpless to the majesty of the universe and its power, but we can marvel at it by watching pretty lights in the sky. So, be sure to check the aurora radar on the off chance that you’re able to watch our magnetic field do its thing!
Thanks to Christopher for the topic recommendation!