Light pollution: an aurora hunter’s foe

There are several things that can really frustrate the avid aurora hunter: dead camera batteries, cloud cover, and that pesky thing called light pollution.

Light pollution is the name for the brightening of the night sky due to the presence of man-made sources, e.g. street lamps, high-rise blocks, or gas flaring from nearby petrochemical plants. We don’t really class events such as Super Moons as light pollution as they make up part of the natural night sky.

In a recent study on light pollution, the authors found that on clear, moonless nights the urban sky was often 20 times brighter than the natural level of darkness.

In clear and moonless nights the zenithal night sky in the analysed urban settings is typically 14–23 times brighter than expected from a nominal natural dark sky

These brighter night skies have some big side-effects. It is estimated that 60% of Europeans are now unable to see the beauty of the Milky Way. It affects your chances of seeing the aurora too as light pollution is often brighter than the aurora and so may wash out our favourite natural spectacle.

But, perhaps more worryingly, it isn’t just a case of us missing out on the beauty of the night sky. Light pollution could affect our health too. It has certainly been shown to affect the wellbeing of animals, including birds, bats, and even fish. Even the new LED street lamps, which save energy, aren’t without their drawbacks.

Map of Europe’s artificial sky brightness, in twofold increasing steps, as a ratio to the natural sky brightness (Falchi et al., 2016).

Map of Europe’s artificial sky brightness, in twofold increasing steps, as a ratio to the natural sky brightness (Falchi et al., 2016).

Light pollution under cloud cover

The intensity of light pollution increases during cloud cover. Light that would normally escape into our atmosphere and out in to space gets reflected by the clouds. In fact, cloud cover can increase the amount of scattered light by a factor of 25!

The presence of clouds in urban areas strongly enhances the amount of scattered light, easily reaching amplification factors in excess of 25, in comparison with the light scattered in the same places under clear sky conditions.

Light pollution under cloud cover is particularly tricky for aurora hunters. Not only is the aurora not visible through cloud cover, light pollution reflecting off the clouds can look a lot like aurora.

Two simple tips to remember though: aurora cannot be seen through clouds, so look for stars, and the aurora is never orange (but streetlamps are!).

Combatting light pollution

We can all do our bit to help combat light pollution. Things like turning off unnecessary lights will not only save you money but will help with light pollution too. Of course, the biggest light pollution sources aren’t at your home but often at places of work. Encouraging companies to take action, like this petition are a start. The UK government is taking steps.

In 2014, the Government published a policy update, ‘Artificial Light in the Environment’, highlighting the steps that have been taken to reduce artificial light pollution. The update is available to view at: www.gov.uk/government/publications/artificial-light-in-the-environment-policy-update.

And you may have heard about that time Reykjavik (the capital of Iceland) turned off all street lighting so its residents could witness the aurora. How awesome is that?!

Spectacular #northernlights tonight in #Reykjavik #Iceland 🙌🙌🙌

A post shared by Daði Guðjónsson (@dadigud) on

In the meantime…

To hunt aurora, you’ll need to find a place with little or no light pollution. This may take some exploring on your part. Find local spots away from big cities or factories. Head out to local dark sky discovery sites. Ask others on our Facebook page and have a look at our top spots page. If you’re lucky enough, you might just get away with a bit of light pollution and still get to see something like this…

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  1. Pingback: Did I photograph the aurora or was it something else? | AuroraWatch UK

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