A WAY TO GREEN LIGHT...TAKING PICTURES OF THE AURORA BOREALIS
Aurora Borealis...every landscape photographer's heart leaps at the mention of these two words. I think I'm not wrong when I say that every landscape photographer would like to not only see the Northern Lights, but also photograph this phenomenon. First of all, let's talk about what the Northern Lights is and how it is created.
The Aurora Borealis, or the Northern Lights, is the collective name for light phenomena occurring in the atmosphere at altitudes between 80 and 1000 km, but most commonly in the ionosphere about 100 km above the earth. The Aurora Borealis is manifested by broad bands of colour in the sky at high latitudes. The southern aurora is referred to as the "Aurora Australis", the northern aurora as the "Aurora Borealis", but it is essentially the same phenomenon.
HOW THE AURORA BOREALIS IS FORMED?
Due to irregularities in the Sun's magnetic field, sunspots appear on the Sun, rising to the surface and bursting like bubbles in a liquid. As they die out, some of the sun's plasma "splashes" out into space, creating a solar flare, or prominence. The resulting cloud of solar wind particles is made up of positively charged protons (the nuclei of the hydrogen atom) and alpha particles (the nuclei of the helium atom), which travel through space at speeds of up to 500 km/sec and reach the Earth within a few days. If it encounters the Earth's magnetic field on its journey, some of it is captured and spirals towards the Earth's magnetic poles. There, the solar wind interacts with the atmosphere, stripping electrons from oxygen and nitrogen molecules to form positively charged atoms (ions). The stripped electrons are pulled back by the attractive force of the protons in the nucleus of the atom, braking sharply and emitting electromagnetic waves of light that we see as the Aurora.
The Aurora can be of many different kinds. What do I mean? The usual colour of the Aurora is green (with a wavelength of 557.7 nm - nanometres) or red (630.0 and 636.4 nm). However, the colour violet can appear at 470.9 nm, 427.8 nm and shorter (invisible) wavelengths of 390.5, 357.8 and 337.1 nm. Less frequently we can register yellow colour. Nevertheless, the spectrum of the Aurora is quite complex, as the energy of the radiation is distributed not only in the visible part of the spectrum, but also in the infrared and ultraviolet regions of the spectrum.
AURORA VERSUS MILKY WAY
The aurora can therefore not only have a variety of colours, but more importantly it appears differently in the sky each time. Sometimes it looks like a motionless green column that simply "sticks" in the sky for long minutes, virtually motionless. At other times it oscillates across the sky like a curtain against which a strong wind is leaning. It can be completely shapeless or, on the contrary, it forms patterns over which the eye passes. I've even seen the Northern Lights appear right next to the Milky Way. And it was the red spectrum from the edge of the aurora that painted the entire Milky Way red, as if a strong red spotlight had been shone on it (see photo). The first time I was amazed by this was last year in Iceland, this year on a photo expedition in Lofoten I was not so surprised by the red Milky Way :)
AURORA PREDICTED...
Predictions of Aurora occurrence will give a big clue as to what may be over our heads. They can't be relied upon 100%, but thanks to modern measurement technology, the occurrence of the Aurora can be predicted fairly well. Basically, the two main models we use most often today are the auroral oval and the KP Index. The oval is determined from data from the NOAA POES satellite. The KP Index then simply expresses how low latitudes the Aurora will appear.
Monitoring solar activity is also an important part of aurora monitoring. A scale of Normal, Active, M Class Flare, X Class Flare!, Mega Flare! has been created for orientation, and if the last grade is reached, there is a chance of observing the aurora even in the heart of Europe. In addition to this indicator, there is also geomagnetic activity. Here the scale is only three points: Quiet, Unsettled, Storm.
As mentioned above, the main contributor to the Aurora is the solar wind, which is measured in several categories. The most important are the particle density, the speed of the wind itself, and its polarity, The greater these values, the stronger the wind and the more likely an aurora is to occur. This data is measured by satellite. The resulting values also allow us to calculate how long it will take for the particle flux to reach us. All of these measurements have one primary goal: to determine when, where and how intense the aurora will appear. In central and western Europe the Aurora is very rarely visible. Statistically, during one decade, the aurora can be observed 5-8 times there. In order to be relatively certain, the KP Index must exceed degree number 8. In the case of monitoring solar activity or geomagnetic activity, it must always be the highest degree, i.e. Mega Flare! or Storm. But definitely don't expect to see the spectacle overhead in the central Europe that we know from photos from the Norwegian or Iceland. If the Aurora is already visible here, it is very faint indeed, often not even visible to the eye, or it appears as a bright area above the horizon that can easily be mistaken for light pollution.
WHERE TO GO FOR THE NORTHERN LIGHTS?
To have a chance to see the Aurora in its full power, we need to go to more northern locations. Iceland is one of the most frequently visited photo locations, followed by the north of Norway. We also need to consider carefully what time of year we choose. In general, first of all, it must be dark at night. This is logical, of course, but it is important to be aware of the existence of the so-called polar day, i.e. the period when the Sun does not set below the horizon beyond the Arctic Circle and darkness does not set in. In the Norwegian north, the polar day is limited to mid-May to late July. The ideal time for Aurora viewing in suitable northern locations is roughly from October to March. Furthermore, we should go out for photography on days when the Moon is not shining. The intensity of its radiation makes the Aurora experience highly relative. And of course we should head north on days when the KP Index is going up. If we are lucky enough to have, say, a clear night in Iceland without the Moon, but the KP Index is 2, we are likely to see the Aurora, but very faintly. In a geomagnetic storm of degree 2 (KP 6), not only will the Aurora be visible much further south, but its intensity will be unparalleled and we will see an unadulterated spectacle overhead in the same place in Iceland.
There are plenty of apps or websites for tracking solar activity, or the ability to see the aurora. The most famous website is probably the Aurora Service. Among mobile apps we can mention Aurora Notifier, Northern Eye, Aurora, Aurora Companion, Norway Lights, etc. Most of these sources include all of the above aspects, i.e. KP Index, Auroral Oval, solar and geomagnetic activity, solar wind intensity, etc.
WE TAKE PICTURES OF THE AURORA
Now the crucial part, namely how do wephotograph the Aurora? Difficult. You probably wanted to hear a different answer, but there it is. In particular, if the Aurora is fast (that aforementioned curtain in the wind), then we have to allow for times on the order of units of seconds, that is, if we want to capture the sharp edges of the Aurora. However, if we only expose for a few seconds during the night, then logically we have to raise the ISO to quite high values. Not to mention, of course, the need to properly expose the landscape and the almost inevitable need to use multiple planes of focus. This is probably the reason why we can see plenty of Aurora photos in online galleries, but not at photo exhibitions. It's a bit of a challenge to take not only visually pleasing, but also technically good photos of the Aurora on a moonless night. One of the solutions is the approach that my colleagues and I took on a photo expedition to Norway. Namely, we went to take photos in early April, almost after the Aurora season. However, in a period when the astronomical twilight is no longer occurring in the north and the sky is still relatively decently bright long after sunset. This timing allowed us to expose the Aurora at a relatively low ISO. Another option is to use multiple exposures and average them to remove noise, but not degrade the quality of the photo. However, this assumes that the same celestial patterns appear in succession over time and so is more a matter of chance and a large number of photos.
MYTHS AND MISTAKES
Myths and mistakes. I have registered several half-truths or misconceptions in connection with the Aurora Borealis. I will mention at least some of them.
The Aurora Borealis is not visible to the eye, only a camera can capture it. I have already debunked this myth in a previous text. Yes, if the KP Index is low, or the other parameters mentioned above are low, then the Aurora will be difficult to see. However, just catch KP 4-5 in Iceland and you feel like you can touch the Aurora and it dances across the sky so that you don't know whether to take a photo or just stare at the sky first.
The snow in photos with the Aurora can't be green. Wrong. Again, if the Northern Lights is intense, then it can easily turn reflective areas green, purple, etc. So this is true for both snow and especially water surfaces.
Aurora cannot cast a shadow. It can. Just be lucky enough to catch the intense Aurora Borealis and you'll suddenly see ice floes on the surface of a glacial lake with shadows, even though the moon isn't shining.
Seeing the intense Aurora Borealis is a truly surreal experience that you just can't get enough of. Perhaps only Norwegians or Icelanders are left cold by the Northern Lights. Although last year in Iceland during KP 8 I ran into some local photographers at Lake Jökulsárlón. The whole sky was green, with a deep yellow here and there that made it look like a chemical factory had exploded. I didn't know where to point my camera first or what part of the sky to watch. And the "locals" commented that it was quite nice:)
