The red glow in the sky grew and lengthened, the lower edge twisting into a bright band against the darkness. Slowly the colours rippled and broke and reappeared elsewhere. Pillars of red streaked down from above like blood dripping from the heavens. The aurora borealis had made an appearance in rare and spectacular form: the blood aurora.

So opened series two of Fortitude last week, a popular TV series set in a fictional town in Arctic Norway. But a red aurora is a real and spectacular scientific phenomenon, and one steeped in mythology.



The aurora is a natural light display that occurs in the polar regions. It is caused by charged particles from space catapulted down magnetic field lines into our upper atmosphere, where they collide with oxygen and nitrogen atoms to produce light. This process is driven by energy from the sun, which comes as a stream of charged particles called the solar wind that interacts with Earth’s magnetic field.



The aurora is most often seen as a green colour in an arch or a band across the sky, perhaps rippling or twisting. To achieve a brilliant red or the fabled violets or crimsons, the aurora generally requires more energy and is much more rare.

The light from the aurora stretches up hundreds of kilometres in the atmosphere. Green light is produced lower in the atmosphere, at around 100 kilometres (62 miles), while red is seen higher, at 200–300 kilometres (124–186 miles). Pictures of aurorae taken from the International Space Station show clear curtains of light stretched out in a bright green that fades up into red, and then fades out altogether. The light is produced in rings around the poles, generally covering the latitude between about 65 and 75 degrees.

When there is more energy coming from the solar wind to drive the auroral processes, the aurora will be brighter and more colourful. Also, the rings around the poles expand and widen, so the northern lights can be seen at lower, more temperate latitudes. Very occasionally aurorae may even be seen in central Europe or the mid United States.

On these occasions, the aurora will likely be seen red in these lower latitude locations. Viewers will be looking north and seeing the top of the auroral curtain with the green lower part obscured by the surface of the Earth.

Many historical writings on the northern lights seen at temperate latitudes describe some sense of foreboding or see the display as a portent or warning, usually with a military significance. This may be due to their colour as well as the rarity of the sight.

Being redder in colour, lower-latitude aurorae were sometimes mistaken for fire, or seen as representing blood in the sky. Rayed structure was often reminiscent of military spears; arcs and curves were fiery dragons. Aurorae are said to have foretold the death of Julius Caesar (44 BCE) and presaged the American Civil War (1860), so for millennia the appearance of a red aurora was interpreted as a bad omen.

Up in the far north in a town like Fortitude there is another reason for red aurorae. The fictional town is set on Svalbard, the Norwegian archipelago that sits in the Arctic Ocean east of Greenland between 74 and 81 degrees north. Here it is possible to see what is known as a “day-side aurora”.

Day-side aurorae are only visible during polar night when it is dark at midday. They are less bright than night aurorae and usually red in colour, to which the eye is less sensitive than green, so it was only discovered in the 1960s that the aurora occurs during the daytime too.

Day-side aurorae are caused by charged particles from the solar wind that come in through the polar funnel of the Earth’s magnetic field directly into the atmosphere. They are not catapulted down field lines in the same way that particles are accelerated into the atmosphere on the night side, which is why the light display is not so bright.

So, could the townspeople of Fortitude have seen a bright red aurora or a faint day-side aurora? Either way, the association with blood in the sky and the historical sense of foreboding make it a compelling opening for the Arctic thriller.

Read more about the people, the places, the landscapes, the stories and the science of the northern lights in Aurora: In Search of the Northern Lights by Dr Melanie Windridge, out in paperback on 23 February or go to www.melaniewindridge.co.uk. Dr Windridge can also be found on Twitter