Polar lights

Polar lights are one of my favorite phenomena. They are colorful, hard to catch and still not fully understood! But let’s dive into the science behind them!

If this is too much physics for you, skip to the tl;dr a the bottom of the page for some practical takeaways.


We need to start out somewhere very hot, the sun. Here convections of charged particles (plasma) in the outer parts of the sun cause strong magnetic fields. Sometimes these fields move outwards creating rings that act like rubber bands. These will snap now and then, blowing out great amounts of plasma. These events are called solar flares, or when they are big: coronal mass ejections. The frequency of such events is linked to the suns 11-year cycle as the suns inverts its whole magnetic alignment though the intensity of each cycle varies.Sunspot_Numbers
We may even head into another Maunder-minimum which would be unfortunate for the science community and everyone who wants to see some aurora. The next peak in sun activity is set for 2023.

As you probably have guessed, these solar flares are part of the so called solar wind which ultimately causes the polar lights. This constant stream of mostly electrons, protons and some nuclei such as helium moves towards earth at speeds between 400 and 700 km/s (250 to 430 mps). Now a complicated process of deflecting, magnetic recombination, particle acceleration and other crazy stuff starts. The whole process hasn’t been understood fully and many effects (or theories) have been shown to play a role but how they all interact with each other is mostly unknown! I will try to map out the clearest elements of this complicated process.

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Earth’s Magnetosphere

Coming from the sun we encounter the bow shock about 12.000 km (7500 miles) away from earth. Most low energy particles are diverted by the earths outer most magnetic fields and move around to the magnetotail. Some particles move into the polar cusp, creating the so called day-light aurora which we can obviously not see with our eyes. Other particles will move into one of the two Van Allen radiation belts. These belts hold great amounts of plasma and act as a reservoir for the aroura but are also constantly washed away and then refilled by stronger solar flares.

Fields_in_magnetic_bottlesThese belts as well as the plasma moving into earth’s atmosphere act in as an first approximation like magnetic bottle. These “bottles” are two magnetic mirrors placed together to create a trap for charged particles. In case of earth’s field, the poles act as the mirrors. When an electron moves in a helical (corkscrew) path along the magnetic field he will eventually approach a pole. Here the magnetic fields become denser and thus creating a backwards force on the particles due to the Lorenz force.

Aurora_australis_ringNow there are several conflicting but also non-conflicting theories about why particles on the night side are being accelerate towards the poles which I won’t go into in detail. Fact is that sometimes particles have enough energy to come spiraling as close as 80km (50 miles). This creates a so called auroral zone as seen in this image of the south pole from one of NASA’s satellites. This auroral zone will move towards the equator as long as the particles have enough energy, they will then move to the pole again. So once you’ve experienced some strong polar lights moving southward (if you’re on the north hemisphere), then wait for them to come back!

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Typical green curtains

Generally, we can differ between discrete, often shaped like curtains, and diffuse aurora. The most iconic and frequently seen aurora are green curtains at 100-150km (60-90 miles) due to fairly high concentrated oxygen emitting light at a wavelength of 557.7 nm. These curtains have a sharp cut of at 100km due to a fast concentration drop of oxygen. Slightly below the curtains one may spot some blue due to Nitrogen molecules being the dominant light source. These two colors are considered discrete aurora due to concentration drops or electrons with more or less discrete energy distributions. The most common diffuse aurora is the red emission of oxygen at high levels of altitude. These can be hard to spot by eye because of the dominant green curtains, but can often been seen on the horizon or in pictures due to the cameras better sensitivity (in comparison to our eyes) to red.

Most of these spectral lines are “forbidden”. This is a misleading term; one should rather call them highly improbable, due the selection rules of quantum mechanics. “Normal” emissions function on a nanosecond timescale. The red emission of oxygen however is very slow (107s) therefore this color will only occur in very high altitudes (>150km) where the probability of colliding with another atom is low enough. Otherwise if an excited atom collides, it will transfer energy and will not emit any red light anymore. Of course now and then other colors will appear often due to an overlap of green and blue or red and green etc.

I hope you have enjoyed this little deep dive into the aurora. It is definitely a very active and interesting field of science, be curious and check it out on your own!

Too long, didn’t read:

The next peak of sun activity should be in 2023, so that’s definitely a year to plan some polar vacation. The process of particles like electrons moving from the sun down to our atmosphere is not fully understood. There are indicators for polar lights that you can look up online every night. If you happen to experience strong polar lights moving towards the equator don’t leave! They are probably going to come back to the poles in the next hours.

Cold beauty of Kiruna

If you are one of those people who don’t like destinies just because it is cold there, please stop reading (no just kidding… a bit). But to be fair: If your kind of vacation includes pools, beaches and pina coladas, then you probably shouldn’t waste the time reading on, unless of course you’re as curious as I am and are therefore ready to try something new.

So yea, Kiruna is kind of cool considering its location. Never underestimate distances in Sweden and Norway! The domestic flight from Stockholm to Kiruna took longer than the flight from Hamburg to Stockholm. Kiruna is considered the northernmost town in Sweden and is lies just a bit north of the polar circle. That is the boarder at which one can experience at least one day of total darkness and respectively one whole day of “sun”.

The temperature in October, November, March and April, which are the optimal months to go to Kiruna for obvious reasons explained soon, is about -5 °C on average (23F for silly people). It will be dry, so all you need is maybe two layers for your legs and 3 layers including a good jacket for your upper body.

Getting there is pretty much only possible by plane, with a 90 min flight from Stockholm. About two planes a day arrive and leave in Kiruna. When I went there in 2015 I flew in a propeller plane. So definitely get the right seat and take your camera, you wouldn’t want to miss out on these kind of photos.

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photo credit: wikimedia.org

If you have no Idea what is going on here, you should learn something about the Rolling-shutter-effect before moving on.

Now I must admit I have been a bad storyteller and have been blabbering about this cold place in the middle of nowhere. So why would you even go there?

 


Polar lights, aurora borealis (opposed to aurora australis at the south pole), appear due to charged particles erupted by the sun hitting our atmosphere. They excite atoms as high up as 150 km (93 miles) creating lights that can be seen by the human eye from below. These wonders of nature are strongest in the months I mentioned above. If this hand waving explanation isn’t enough (and it shouldn’t be), check out my in-depth explanation on polar lights.

aurora borealis

Before I had gone to Kiruna I had never taken more than a handful of photos for myself. I used to believe special moment in life shouldn’t be perceived trough a lens but through our naked eye, and I still believe this. But polar lights are actually slow enough to do both!

It is surely not the easiest object to start taking photography serious as a hobby but if you’re fascinated by natures beauty, then you can use that as a stepping stone for photography. If you’re already into photography but have never played around with night-time photos, then you should definitely do that! All you need is a decent reflex camera, optimally with a good light-sensitive chip, a tripod and a shutter release cable (so you don’t move the cam as you start the exposure), then you’re ready to play around with ISO, aperture width and exposure time. As a last notice, always try to integrate some ground into your picture. Our stupid brains need a reference point otherwise no one will know what they are looking at.

OLYMPUS DIGITAL CAMERA

This picture has just a “small” strip aurora and yet several people have asked me if they could use it for their purpose in magazines. So obviously it isn’t only about getting many bright lights into your camera. (Nice brag I snuck in back there, huh?).

Fortunately for us Kiruna has a lot to offer when it’s too bright for polar lights:

The “Institutet för rymdfysik” (don’t just skip that word, try to pronounce it!), the Swedish institute for Space Physics, has its headquarters is Kiruna. They can display a wide range of research subjects from Polar Atmospheric to Solar Terrestrial Physics and are one of the leading providers of Ion thrusters! Actually if you’re looking into doing your SpaceMaster here would be a great place to study. I mean come on, that’s almost as good as Master of Disaster.

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photo credit: wikimedia.org

Moving on to the next space related topic. ESRANGE is a scientific rocket range and research center for high altitude balloons and small rockets such and BEXUS and REXUS, which are projects that are only open to university students! The unique part about ESRANGE is, that they can reclaim the rockets with the experiments because they landcrash on a big area north of Kiruna (yes there is even more land up north) instead of crashing into water. Usually they also tell the Russians before they launch a fast rocket into the stratosphere.

Last but not least you should end your trip with a visit to the biggest iron ore mine in the world. The reason why someone would even consider building a town up there in the beginning of the 20th century is, well… iron. Today they extract gigantic amount of ore from deeper than 1300 meters. If you ever wake up at night or are still awake taking nice photos you may experience some tremors due to the explosion in the mine. The iron ore lies under the city of Kiruna if you go deeper. Thus the company running the ore has to pay half the city money to relocate to a safer part of the city, what iron(y)!


So to sum things up, I hope you could see from the few photos how beautiful it is. I would highly recommend going there as an excursion with your university buds (or anything similar). If you love an adventure, a change in climate and are mildly interested in space science and/or nighttime photography, then this is definitely a place to check out!

Warm travels and stay curious!