Perhaps surprisingly, not everyone has heard of the Aurora Borealis (or indeed the southern hemisphere version, the Aurora Australis). Many of those who have however, have added it to their bucket list to experience. Also known as the Northern Lights among English speakers, Nordlys in much of Scandinavia and rather poetically as Revontulet (the fox’s tail) in Finland, they are both a natural scientific phenomenon and mysterious at the same time. They are the subject of many folklores in native peoples around the world, but what exactly are they?
At its most basic, the Aurora is a light display in the sky, caused by the collisions of electronically-charged particles. These particles originate from the sun. It usually only occurs at high latitudes, but during large solar flares, they have been visible as far south as the Mediterranean and in the last few years, there have been a few occasions, where they have been visible in southern England.
The Aurora can occur at any time, provided it is clear enough and dark enough, but it doesn’t need to be fully dark or fully clear and in fact, the brighter displays can be visible through clouds, The solar wind is a constant presence, but just like terrestrial wind, the speed and strength is variable. The faster or stronger the wind, the stronger the potential display. The solar wind is caused by plasma particles. These particles interact with the upper layers of the Earth’s atmosphere, where they collide with gas particles, causing them to excite. The subsequent release of energy is what causes the lights. If these particles were able to reach the surface, they would cause great damage to the life living on Earth. However, we are all protected by the magnetic field around Earth,which draws the particles to the poles. The area around poles are therefore the best places to view the Aurora. When the number of solar particles increases, the Auroral ring is pushed further south.
There are essentially three colours of light produced, green is the most common, followed by red and purple. The precise colour is down to individual perception and strength of the Aurora. The human eye isn’t very good at seeing colour in the dark, so any weak displays will appear like a white glow. Stronger displays will show evidence of colour and some people can detect colour more readily than others. In addition, strong displays also show visible movement, producing shapes. Camera sensors are much better at picking up the colours and images are therefore usually more vivid than what is seen by the naked eye. The different colours are as a result of reactions with different gases and at different heights in the atmosphere. There is much information online, but the two main gases involved are oxygen and nitrogen.
Predicting the Aurora
Finding Clear Skies
The first hurdle is being able to find clear skies. This means knowing a bit about the weather and you almost start becoming an amateur weather forecaster. Often, when chasing the Aurora, you are chasing the gaps in the clouds. Contrary to popular belief, you don’t actually need clear skies to be able to see the Aurora, you just need to have skies clear in the right place. The Aurora can appear anywhere in the general direction of northeast to northwest (although when strong, it is pushed south and may cover the whole sky), so if you have clear skies to the north, you still have a chance. Sometimes you just need a few gaps and that can have some interesting effects, especially in photographs.
Knowing when it Will Happen
The aurora can happen at any time of the day and at any time of the year, but if it isn’t dark enough, then you won’t see it. There are some general rules to indicate the best chances, but they aren’t hard and fast.
Around the poles, in the summer, hours of darkness are limited or non-existent, so realistically, the Aurora is only visible between Autumn and Spring. Also, due to the angles, the strongest part of the Aurora is on the opposite side of the Earth to the sun, so the best chance is often around midnight. Finally, for reasons that aren’t fully understood, activity is often higher around the vernal and spring equinox. My theory is, that it is because the tilt of the Earth means that the Arctic Circle is roughly perpendicular to the sun at those times, but of course, there is no way that I can prove it.
Just like weather on Earth, the Solar activity also varies. There are ways to predict the activity, but no real way to predict solar flares, beyond likelihood. The presence of sunspots and some other solar features increase the chance of solar flares and the subsequent coronal mass ejection (CME) results in increased plasma heading out from the sun, which may or may not be Earthbound. There are two satellites positioned to detect inbound flares and these can be used as an early warning. There are many Apps produced that use these satellites and other measurements to predict the level of Auroral activity. Activity is measured by the kP index, which is a scale a bit like the Beaufort wind scale. It is measured from 0-9, with kP 9 indicating severe storm activity and a high chance of Aurora, even at lower latitudes. My favourite App is one called Aurora Alert, this is a paid for alert, but there are also some free ones available. This app uses a number of different datasets, but one of the useful ones is the Wing kP, produced by the NOAA Space Weather Centre in the US.
There are a few other useful sites, but SolarHam has a wealth of data and explanations.
The most important piece of equipment is a tripod. Any good tripod will do, but it must be sturdy and it may be necessary to secure it in windy conditions, so rope or string may also be a useful addition to your camera bag. It is also best to have a cable release.
The general rule is wider and faster. That is, use lenses as wide-angle as possible, with an aperture as wide as possible. Full frame sensors also work better than crop sensors, as they have a wider field of view for a given lens, they are also generally better when using high ISO settings.
I currently use a Canon EOS 5D MkIV, which has very good high ISO results, but I have also used both the 5D MkII and MkIII, as well as a 7D. My first choice lens is the Canon EF 24mm f/1.4, although I usually stop down to f/2, as the wider apertures tend to distort the stars. I have also seen very good results from a Zeiss 21mm f/2.8 and a Tamron 24-70 f/2.8, as well as fisheye lenses. The Aurora can sometimes cover large areas of the sky and for best chance of capturing as much of the display as possible, it is best to use 24mm or wider (full frame equivalent). If using a crop sensor, then try to go wider if possible. The Aurora can often produce movement and this produces shapes and waves. To get the best chance of capturing these shapes, you want to keep the exposure time as short as possible. Thirty seconds is the longest, but for best results, it is best to keep exposure shorter than 15 seconds. If you can get down to 3-4 seconds, then even better. To get these exposure times though, you need a sensor that can produce low noise images at ISO settings of 800-3200 (lower is of course always better) and a lens with a widest aperture of f/2.8 or greater is best.
One final note, never use filters when photographing the Aurora, as they interfere, producing weird effects.
Technique is very important when photographing the Aurora. A steady camera is one that gets the best results. If shooting single shots, then using mirror lockup is desirable, however, when shooting on continuous, this becomes more complicated and it may be easier to just keep continuous shooting without mirror lockup. Many people shoot timelapse sequences and continuous shooting will allow you to do this, plus it will also allow you to just forget about the camera and enjoy the show without the stress of setting the camera up to get some decent images. This is particularly important if it is your first time seeing the Aurora. If you’re going all that way to see the Aurora, then you might as well enjoy the show.
The first step is to find a good location, with clear skies and a good chance of seeing the Aurora. Once the Aurora starts, you can have a good idea of compositional choices available. Next follow these steps to get the best images you can.
- Point the camera in the direction of the Aurora (on a tripod), taking into account any landscape features that may improve the composition.
- Point your camera towards the brightest star you can find and switch to Liveview.
- Zoom in to the maximum magnification and adjust the focus, so that the star is a pinpoint of light.
- If possible, tape the lens, so that the focus doesn’t alter.
- Position the camera to your preferred composition and tighten the tripod, so that it doesn’t move.
- Set the ISO, aperture and exposure time (it is always best to use manual mode for best results when shooting the Aurora) and take some test shots.
- Adjust your settings as necessary. Try to keep the ISO as low as possible and the exposure time as short as possible. This will always be a compromise, unless it is a very strong display.
- Set your shutter going on continuous and enjoy the display.
One of the biggest enemies of Aurora chasers and photographers is light. Light pollution can be a real pain, but it can also be good for photography. Many say you can’t photograph or see the Aurora with a full moon. This isn’t strictly true. The full moon does make it harder to see and photograph the Aurora, but if it is a strong display, then it can produce some wonderful results, as it will light up the foreground, turning the Aurora image into a spectacular landscape photograph. Light pollution can also be a problem. With cloudy skies, it can be a nightmare trying to get an accurate colour balance, as the clouds will tend to turn a horrible muddy orange colour, which means a lot of post production time, trying to remove the colour cast. Bring along some clear skies though, and the lights from a small hamlet can produce interesting reflections in a nearby body of water, greatly enhancing your compositional opportunities.
The Aurora borealis is a wonderful natural phenomenon and one I have spent hundreds of hours photographing over the last eight years. If you get the chance to see it, then take it and don’t get too hung up on taking photographs. Enjoy the show and happy photography.