Wild Side: Natural light shines on Martha’s Vineyard

With surprising regularity, guests at our house in Oak Bluffs walk out onto our deck at night, look up, and exclaim something like, “Wow! I’ve never seen the Milky Way before!” I don’t know which impresses me more: The fact that our humble abode on the fringes of the O.B. Metropolitan Area offers such good viewing conditions, or the fact that so many folks in America live in places with viewing conditions so bad that they can’t even see our own galaxy.

Our night sky is hardly pristine: the glow from Falmouth and Hyannis is apparent, especially when humid air diffuses the light. And even the smaller town centers on the Island itself dim the stars to a degree. But relative to most of southern New England, the sky over most the Vineyard is impressively dark. And on a clear, dry night, the up-Island view of the sky is astounding: an incomprehensible number of stars, the brightest seemingly close enough to touch, the faintest ones infinitely distant.

I’m an advocate of darkness for two reasons: its benefits for wildlife and its benefits for humans. The first may be the less important of the two, but there is no question that light pollution degrades the natural environment. The glow of artificial light expands the zone of human influence, deterring some animals and attracting others. Most at risk are probably moths, whose simple nervous systems often experience an unfortunate attraction to artificial light.

What draws moths to lights is not fully understood, but it’s worth remembering that moths evolved in a pre-human world that included very few sources of bright nocturnal light. Entomologists speculate that moths evolved to use one of these, the moon, as an aid for navigation. The moon is distant enough so that its apparent location doesn’t change as we move; therefore, by keeping the moon in a constant place in its field of vision, a moth can infallibly fly a straight line.

A streetlight, much closer than the moon, does change its apparent location as you move. But a moth’s brain, which evolved in the absence of nearby light sources, can’t quite grasp the concept. In trying to keep the light at a constant angle — say, directly to the left — a flying moth ends up circling the light rather than continuing on a straight line. Thus, an artificial light ends up with a swarm of disoriented moths around it, moths that might better spend their time mating and laying eggs in a darker landscape.

Scientific evidence that artificial lighting harms moth populations is rather thin, but then, it’s a hard question to study. Intuitively, I can’t believe that pulling moths out of their natural habitat does them any good. And even if the impact of a single light on moth populations is miniscule, it is magnified by thousands across the Island.

The second argument for darkness, its benefits to humans, is still more compelling. Optimized for diurnal activity, we find night mysterious, maybe even a little threatening. For me, that reestablishes a healthy balance in how I relate to nature: darkness reminds us that we’re animals, with physical limitations, and that a natural world exists that we can’t fully understand. And a starry sky is one of the great pieces of poetry the natural world offers us, an unending source of wonder and inspiration.

A certain amount of lighting of our homes, streets, and public places is necessary, of course, for safety and practicality. (Though I think that maintaining a community based on mutual respect is a better deterrent to crime than a panoply of floodlights.) And a certain amount of light will inevitably spill from its target onto the surroundings. But we could easily put ourselves on a trajectory toward darker nights.

The first and easiest step would be simply turning unneeded lights off, indoors and out. Businesses and municipalities could ask themselves if parking lots really need to be illuminated at 3:00 in the morning. When new lighting is installed, we should ask how bright it really needs to be, and new fixtures or replacements for old ones should be designed to direct light where it’s needed and shield it from where it’s not. Finally, for outdoor lighting, yellow bulbs (best may be yellow compact fluorescents, now quite widely available), since studies have shown that most insects are less attracted to yellow light than to other colors.

I don’t expect to see the Milky Way from the sidewalk along Circuit Avenue. But seeing it from my backyard is one of those subtle but powerful pleasures that make life on the Vineyard rewarding. We could set as a goal keeping our galaxy visible where it is now, and trying to expand the portion of the Island where the infinite night sky looks the way it should.