Let There Be Night

"People think they know darkness, and that they experience darkness everyday, but they don't, really."

Across the United States, natural darkness is an endangered resource. East of the Mississippi, it is already extinct; even in the West, night sky connoisseurs admit that it's quicker to find true darkness by flying to Alice Springs, Australia, than traveling to anywhere in the lower forty-eight.

Ever since the nation's first electric streetlight made its debut in Cleveland, on April 29, 1879, the American night has become steadily brighter. In his new book, The End of Night: Searching for Natural Darkness in an Age of Artificial Light, Paul Bogard aims to draw attention to the naturally dark night as a landscape in its own right -- a separate, incredibly valuable environmental condition that we overlook and destroy at our own peril.

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Poster designed by Tyler Nordgren, author of Stars Above, Earth Below: A Guide to Astronomy in the National Parks.

Venue took the opportunity to visit Bogard in his office on the campus of James Madison University, in Harrisonburg, Virginia, to learn more about nocturnal America and its dark skies -- and what we have lost by dissociating the two.

Our conversation touches on the difficulty of measuring and preserving such an ephemeral quality, as well as the ecological and health consequences of endless artificial light, with speculative detours into evolutionary shifts in human vision and the possibility of preserving Las Vegas (the brightest pixel in the world in NASA photographs) as a "light pollution park."

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The Bortle scale was originally published in Sky & Telescope magazine in 2001. It classifies the darkness of skies from point of view of an astronomer, ranging from 1 ("an observer's Nirvana!") to 9, in which "the only celestial objects that really provide pleasing telescopic views are the Moon, the planets, and a few of the brightest star clusters." This illustration of the scale comes via Stellarium.

Nicola Twilley: Darkness is easy to overlook, if you'll excuse the pun. How did you go about structuring the story of such a familiar, yet intangible quality?

Paul Bogard: People think they know darkness, and that they experience darkness everyday, but they don't, really. That's one of the reasons I borrowed the Bortle scale for the table of contents. I think John Bortle's point, when he created this tool for measuring the darkness of skies, was that we have no idea what darkness really is. We think night is dark -- full stop, end of story. But, on the Bortle scale, cities would be a Class 9 -- the brightest. Most of us spend our nights in what he would call a 5 at best, or more likely a 6 or 7. We rarely, if ever, get any darker than that.

Until the coming of electric light, people experienced a darkness that Bortle would classify as 2 or 3, every night. What I tried to do in the book is to show that difference, by working my way down from places that are bright to those that are less bright, but also by talking to people who are living and working in those places.

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Left: Winter constellations in a Bortle Class 4 or 5 sky. Right: The same constellation panorama in an urban, Class 8 or 9 sky. Illustrations by John Bianchi from Exploring the Night Sky by Terence Dickinson, Sky & Telescope, February 2001.

Twilley: It's interesting that, in order to see the nuances in darkness, we need to measure and name it. It was certainly a revelation to me to read in your book that twilight has three stages -- civil, nautical, and astronomical, with civil being when cars should use headlights, nautical meaning that enough stars are visible for navigational purposes, and astronomical referring to the point at which the sky is dark enough for the faintest stars to emerge. Previously, I had thought of twilight as a single condition on the light-to-dark spectrum, rather than a multiplicity.

Bogard: For sure. For me, one of the reasons why identifying different depths of darkness is so important is that we don't recognize that we're losing it, unless we have a name to recognize it by. It's also a way to talk about what we might regain.

That's also what the National Parks Service Night Sky team, who I describe in the book, is trying to do with their sky quality index. If you're charged with preserving darkness as natural resource, unimpaired for future generations, then you need to be able to put a number on the level of darkness. You need to be able to see and measure any losses before you even know what you're trying to protect.

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A member of the Night Skies team setting up the wide-field CCD camera that the National Parks Service uses to measure light pollution, at Homestead National Monument, Nebraska.

Twilley: It's astonishing to read the description of a Bortle Class 1, where the Milky Way is actually capable of casting shadows!

Bogard: It is. There's a statistic that I quote, which is that eight of every 10 kids born in the United States today will never experience a sky dark enough to see the Milky Way. The Milky Way becomes visible at 3 or 4 on the Bortle scale. That's not even down to a 1. One is pretty stringent. I've been in some really dark places that might not have qualified as a 1, just because there was a glow of a city way off in the distance, on the horizon. You can't have any signs of artificial light to qualify as a Bortle Class 1.

Presented by

Geoff Manaugh & Nicola Twilley

Geoff Manaugh writes at BLDGBLOG. Nicola Twilley is the author of Edible Geography. In 2012-13, they are traveling to sites around the United States with their portable-media project, Venue.

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