[Odysseus] never closed his eyes, but kept them fixed on the Pleiades, on late-setting Bootes, and on the Bear – which men also call the Wain, and which turns round and round where it is, facing Orion, and alone never dipping into the stream of Oceanus – for Calypso had told him to keep this to his left.
–The Odyssey (Book 5) Homer
Celestial navigation is as old as the stars (I apologise, I couldn’t resist the pun!). The night sky was used as a navigation tool long before compasses were invented, and it helped most of the ancient explorers gad about the globe without maps. Even today, anyone who doesn’t trust Apple Maps knows how to orient themselves using Polaris in the northern hemisphere and the Southern Cross in the south.
But, like a lot of things we think we’re pretty good at, animals figured it out long before we did. Quite a few interesting experiments have shown that birds or animals can navigate using the stars and now, the dung beetle has become the first insect proven to navigate by the stars (although, maybe the ancient Egyptians already knew this when they elevated the dung-rolling scarab to sacred status?).
Marie Dacke and her colleagues designed an experiment to test how dung beetles used the night sky to roll away from the dung heap. Dung beetles are pretty serious about their poo, and when there’s a whole group of them on a fresh heap, any given beetle is hardwired to get their ball rolling and get out of there because the competition can get pretty dirty (…sorry, there I go again!).
Using field and planetarium lab experiments with various states of ‘night sky’ overhead, Dacke’s research group tracked beetle movements away from a dung pile inside a test arena – under the full starry sky, beetles took about 40 seconds to get out of the arena, compared to about 120 under complete darkness. More interesting, though, are the patterns of the beetle tracks – when no stars are visible, the beetles wander about in vain, going around in circles and often ending up back at the dung heap they’re trying to escape (have a look at Figure 1 here).
Any nocturnal animal, bird or insect needs to see the stars or the moon to navigate and orient themselves – this in turn affects their foraging, reproduction, communication and, ultimately, their survival. If the stars disappear from our skies permanently, these animals will most likely follow.
Sadly, light pollution has conquered the stars in many parts of the world. Recent estimates indicate that 80% of the United States and 60% of Europe live under a night sky that is brighter than the light of a full moon in the clearest conditions! One fifth of the world’s population can’t even see the Milky Way anymore. Even worse, 40% of the US and 17% of Europe will never truly experience night time – the brightness of their night sky is above the night vision threshold, so their eyes will never need to adapt to seeing in the dark.
So, for the sake of our children getting to see the magnificence of the Milky Way, for the sake of the dung beetles and every other nocturnal navigator, we need to dim the lights.
And here’s a great incentive: Venice is the only city in Italy where you can view the Milky Way from the city centre on a clear night. Why? Because of the “unique low-intensity romantic lighting” that the city is known for.
© Manu Saunders 2013