The northern lights (aurora borealis; also southern lights for the southern hemisphere, aka, the aurora australis) are one of the most sought-after phenomena in the night sky. Casting bright, colorful lights from above, they have entranced civilizations for countless years. Thanks to digital photography, photographing them has recently become one of the most exciting objects to capture. Unfortunately, few people really know how to take advantage of the opportunity, so hopefully this will help you capture them next time you’re out. The term ‘northern lights’ can be replaced at any point with ‘southern lights’. I’ll use the terms interchangeably. Likewise, I’ll also use auroras where either southern or northern lights could be used. Since it all refers to the same phenomenon, I often switch between using them, though it all means the same thing.
Northern lights can only be seen in the extreme north (Canada, Alaska, etc.)
The northern lights can actually be seen anywhere, provided the conditions are right. They’re caused by energy from the sun reacting with our magnetosphere, an invisible (to us) field around the planet that is created from our planet’s magnetic core. Most of these reactions are most visible around the Arctic and Antarctic Circles since it doesn’t take much energy to spark them, making the aforementioned locations the most ideal for viewing them since they’re visible there the most. However if the sun produces a solar flare that happens to be targeted toward Earth, that extra burst of energy will hit the magnetosphere and will react much farther south than normal. Under these conditions, the northern lights can be (and have been) viewed as far as south as Alabama or Arizona, and with a strong enough impact, even farther south.
The auroras can only be seen in the winter.
Since the sun doesn’t experience the seasons in the same sense as we do, there’s no reason that the auroras would only be visible in the winter. In fact, the magnetosphere is always working year-round. You would definitely notice if it weren’t. Similarly, a solar flare can occur at any time of the year, thus sparking the auroras farther south at any time during the year. The myth that they can only be seen in the winter comes from the fact that the locations mentioned above are ideal for viewing them, and since those locations get 24 hours of daylight in the summer, it never actually gets dark enough to see them in summer. It’s not until winter begins creeping in that there’s enough darkness for them to even become visible. So, in fact, the two myths essentially work together to reinforce themselves, but as you can see, are easily debunked.
How to Look for Northern Lights
Since most of you will be reading this in a location that doesn’t regularly experience the auroras, you won’t know if they’re out or not unless you go outside and look. Of course there is a better way though in case they may be faint or you might be experiencing variable weather. A site I check (multiple times) every night is called SpaceWeatherLive.com. At first glance, you probably won’t see anything that looks helpful at all, but making sense of the graphs displayed is easy enough, and I’ll do my best to keep it simple so that after a few checks, you’ll be able to simply glance at it to know if you should get excited or not like a photon in the magnetosphere reacting to charged energy from the sun (that means geeking out for northern lights enthusiasts). Unless you’re really into getting into the nitty-gritty of it all, don’t worry too much about the abbreviations and scales. The important part is just knowing what to look for on those scales.
The primary indicator, though certainly not the only, is the Kp Index. This is the data that many apps and other websites use to predict whether or not you’ll be able to see them. The Kp Index is an arbitrary scale measured from 0 to 9. As you can see from the graph, a reading of 0 indicates that even areas near the Arctic/Antarctic Circles would have difficulty seeing the lights. 1 and 2 would indicate regular activity and good visibility nearby those areas. For the northern lights to begin being visible in the continental United States, the Kp needs to get to at least a 5 or so. A 9 would allow as far south as Mexico to see them, though those events can be pretty rare, as you might have heard (or not heard, more appropriately).
Easy enough, right? Not quite actually. If I were to only follow the Kp Index, I would therefore have to wait until it was at 6 to see them here in Jackson Hole, Wyoming, and yet, my camera has picked them up (and on rare occasions, I’ve personally seen them) when the Kp Index was less than 4. How can that be possible? Simple: All those other graphs have just as relevant data as the Kp Index. Two other graphs on the site are the Bz and Bt, which measures the direction and strength of the Interplanetary Magnetic Field respectively. If the Bz has a strong southerly direction, such as something lower than -10nT, it’s worth going out and grabbing a test shot to see if your camera picks up anything. Likewise, if the Bt gets above 25nT or so, you can start to get excited. The Bz and Bt are just two more graphs that could make it possible to see the auroras even if the Kp Index is weak, but there are in fact even more ways to see them.
The speed of the solar wind (the first graph on the site) can also have an impact in the visibility of the auroras. If the solar wind picks up to 600 or even 700 km/sec, then it’s also possible to see them. Ideally all of these factors will work together so that they will all be spiking during a period of activity, however it doesn’t always work that simply, which is why I’ve outlined the various parts of the data that you want to be aware of. Again, (unless you really want to know) it’s not necessary that you understand what it all means, it only matters that you know what to look for in the graphs. Once you see them flaring up and have some relative basis for comparison of them all, they’ll start to get a lot more meaningful.
Settings for Northern Lights
Assuming you’ve read the previous sections, you should be very familiar about your settings depending on whether there’s moonlight or not. This will be important because we’ll be changing up the rules a little bit for the auroras, but the same general understanding still applies. Thus far, shooting at roughly 20 seconds or so has been ideal to bring out and expose many dimmer stars and to create a more dynamic and interesting night sky. If we stick to those same formulas however, our auroras will appear blurred together simply as one glowing blob (which could be interesting in its own way, but not quite ideal in the right conditions).
To get the most out of a good aurora display, you ideally don’t want to exceed any more than four seconds for an exposure. In fact if the activity is good enough and producing enough light, you’ll want to drop it even lower to something like two seconds. This will capture the streaks and preserve their detail rather than blurring them. Obviously, this will cause you to have your aperture as low as it will go with a generous ISO, depending on the proximity of the auroras. If they’re overhead, they should be producing plenty of light so that you don’t need to exceed 2,000. If they’re on the northern horizon however, you’ll probably have to push up not only the ISO beyond that, but also your shutter speed. If you’re viewing them on the northern horizon, the vast distances between you and them will give you a bit of leeway in your shutter speed so that you can push that up to a higher value as well. Often in this case eight seconds can be achieved while still preserving the detail. How so? Consider clouds and/or forest fire smoke. From a vast distance, they don’t seem to change shape very fast. Up close however, such as in fog, they appear to morph with much quicker rapidity. So it is with the auroras as well.
Composing for the Auroras
In terms of a composition with no moonlight, a silhouette works well if the northern lights are at a distance and thus, on the northern horizon. A treeline or mountain range or peak would provide an excellent foreground for such a display. If they’re overhead, you have much more flexibility because the glow will illuminate many features on the ground in the same way that moonlight does. In that case, you could probably get away with a higher aperture and more foreground objects.
If there is moonlight, you not only have more light for flexibility in your exposure, but also your composition as well. This is where you can have a full moonlit landscape, but also include more of the sky than you might normally under similar conditions to allow for the auroras as well.
You should be well-equipped now to not just capture a starry sky or moonlight sky, but now the northern lights if they’re out as well! If you have any questions, please feel free to ask them in the comments below. Otherwise, keep an eye on SpaceWeatherLive.com for your next aurora opportunity!