The Northern Lights - Aurora Borealis

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. There may be greens, purple, red or gold mixed into the show, or it could be a dim shade of green. There is no rule governing 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 things in astronomy, you really 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 we see 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, it causes complex changes to happen to the tail region. These changes generate currents of charged particles, which then flow along lines of magnetic force 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 are very beautiful to look at, however, the invisible flows of charged particles and magnetism that go on at the same time can damage satellites in space and electrical power grids here on Earth. For this reason, scientists are very 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 they're energised by the solar winds.

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 at the same time, 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 up in the atmosphere and are 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 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?

For the best probability of seeing the lights, you want to be under or close to one of the auroral ovals.

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, anytime between dawn and dusk, and are least common in the summertime months. 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, the occurrences of 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 may well be fires that surrounded the edge of the world, 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 a necessity 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 for this, and fisheye lenses are remarkably good as well.

A cable release can be useful to take multiple exposures without touching the digital camera. This not only ensures sharp shots at slow shutter speeds but in addition 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 that your lens is focused accurately before you commit 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 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 stops exposure compensation. Once you've got the basic exposure setting, you'll be able to make the image more interesting by including some foreground subjects. This provides scale and very much improves the entire composition. Moonlit nights might provide sufficient light, or you can "paint" your subject with the light from a torch.