What Causes The Northern Lights - Aurora BorealisWhat are the Northern Lights? When and where can you see the Northern Lights? How often do you see the Northern Lights?
The aurora borealis, often referred to as the Northern Lights (Southern Lights in the southern hemisphere), is a vibrant demonstration of the Earth's magnetic field interacting with charged particles from the Sun. It's also gorgeous and worth braving a chilly evening out when visiting high northern (or southern) latitudes.
What are the Northern Lights?
The northern lights are one of several astronomical phenomena called polar lights (Aurora Polaris). They are shafts, or curtains, of coloured light which can be seen floating in the night sky. The natural light show may be visible for hours or minutes, depending on the conditions. Greens, purple, red or gold may be mixed into the show, or it could be a dim shade of green. No rule governs the northern lights, as with all things in nature.
It is a breathtaking experience for those blessed to see the lights in all their majesty. It is as if the night sky comes alive with colour, dancing in the heavens.
And yes, unlike most astronomy things, you can see the Northern Lights as they appear in photos. There's no camera trickery, fancy techniques or equipment and no post-processing. You really can see them as they appear in photos.
What Causes the Northern Lights?
The Northern Lights from the ground are caused by electrically charged particles from the Sun entering the Earth's upper atmosphere at a very high speed. Auroras are centred on the Earth's magnetic poles, visible in a roughly circular region around them. Since the magnetic and geographic poles aren't the same, sometimes the auroras are visible farther south than one might expect, while in other places, it's farther north.
The beginning of an aurora starts at the surface of the Sun when solar activity ejects a cloud of gas. Scientists call this a coronal mass ejection (CME). If a CME is sent out in the right direction, in around 2-3 days, it will collide with the Earth's magnetic field. The magnetic field is invisible, but if you could see its shape, it would make Earth look like a comet with a long magnetic 'tail' stretching a million miles behind Earth in the opposite direction of the Sun.
When a coronal mass ejection collides with the Earth's magnetic field, complex changes happen to the tail region. These changes generate charged particle currents, which flow along magnetic force lines into the polar regions. These particles give an energy boost in Earth's upper atmosphere, and when they collide with oxygen and nitrogen atoms in the atmosphere, they produce dazzling auroral light.
Aurora is very beautiful to look at. However, the invisible flows of charged particles and magnetism that go on simultaneously can damage satellites in space and electrical power grids here on Earth. For this reason, scientists are keen to understand the mechanics of auroras and solar storms to better predict when our technologies may be affected.
What Causes Different Colours in the Northern Lights
Different ions within the ionosphere make different colours when the solar winds energise them.
The most common colour observed in the Northern Lights is green. When the solar wind excites millions of oxygen atoms within the Earth's atmosphere simultaneously, it excites the oxygen atoms briefly. They then return to their original state and emit the green hue we can see from the ground.
The red light we sometimes see is also brought about by oxygen atoms. These particles are higher in the atmosphere and subject to a lower energy red light emission. The red colour is always there, but our eyes are five times less sensitive to red light than green, so we can't always see it.
On rare occasions, the solar wind is strong enough to excite nitrogen ions. These nitrogen ions emit a purple hue. This is quite a rare colour to see, and in most cases, it only occurs during a particularly energetic show.
Where is the Best Place to See the Northern Lights?
In the Northern Hemisphere, the auroral zone runs along the northern coast of Siberia, Scandinavia, Iceland, the southern tip of Greenland and northern Canada and Alaska. Auroras are visible south of the zone, but they're much less likely to happen the farther away you go.
The Southern Hemisphere auroral zone is most commonly over Antarctica or the Southern Ocean. To see the southern lights (or aurora australis), you need to go to Tasmania, and there are occasional sightings in southern Argentina or the Falklands. Those, however, are rare.
When is the Best Time to See the Northern Lights?
You want to be under or close to one of the auroral ovals for the best probability of seeing the lights.
The northern lights are very similar to other weather patterns in that they can be forecasted and need certain conditions to occur. They can happen anytime you have dark skies, between dawn and dusk, and are least common in the summertime. They can happen all year round but are best seen between September and April.
The Northern Lights in Mythology
Many cultural groups have legends concerning the lights. In Roman myths, Aurora was the goddess of the dawn. In medieval times, auroral shows have been seen as harbingers of warfare or famine.
The Scottish, Irish, English and French all considered the lights an omen of coming strife, while on the other hand, the Scandinavians associated them with bountiful fishing, painless childbirth, and warmth.
Interestingly, Old Norse and Icelandic literature don't mention auroras much. The Vikings thought the displays might be fires that surrounded the world's edge, an emanation of flame from the northern ice, or reflections from the Sun as it went around the other side of the Earth. All three ideas have been regarded as rational, non-supernatural explanations in the Medieval Period.
The Maori of New Zealand shared a belief with many northern people of Europe and North America that the lights were reflections from torches or campfires.
Photographing the Northern Lights
A digital SLR is perfect. It's also beneficial to stock up on memory cards and charged batteries so you can fire at will without having to fret about running out of space or power.
Fast optics are necessary for photographs like this, with an aperture of f/2.8 being the minimum and f/1.4 a bonus. Wide-angle zooms are ideal, and fisheye lenses are also remarkably good.
View my Northern Lights Gallery.
A cable release can be useful to take multiple exposures without touching the digital camera. This ensures sharp shots at slow shutter speeds and leaves you free to view the spectacle as it unfolds within the sky above. You can use a camera self-timer and continuous drive or use an Intervalometer, which will allow you to program exposures and intervals.
You'll need to keep your camera stable to avoid undesirable motion blur throughout long exposures, so mount your camera on a sturdy tripod and a flat solid surface.
To avoid disappointing photographs, ensure your lens is focused accurately before committing to a shot. Set it to infinity, take a test shot, then zoom into the image on the LCD and check the stars for sharpness. To focus on infinity, tape the focus ring in place to avoid accidentally moving it. Focus on the Moon if it's up or lights are in the distance, then switch to manual focus mode. This will lock the lens focus on infinity. Check and recheck your photos for sharpness during the night. It is easy to nudge the focus ring accidentally and ruin all your remaining exposures.
Depending on your camera's functions, I would suggest starting with an ISO of 800 to keep the noise down and shooting with the lens wide open, f/2.8 is ideal, and f/1.4 is even better. Take a test shot in aperture priority mode and view the picture on the LCD. A dark image where the aurora is barely visible is underexposed, so you want to dial in +1 or +2, which stops exposure compensation. Once you've got the basic exposure setting, you can make the image more interesting by including foreground subjects. This provides scale and improves the entire composition. Moonlit nights might provide sufficient light, or you can "paint" your subject with the light from a torch.
