How FLAGSTAFFis preserving DARK SKIES A star party and world-leading community are keeping the hometown of Lowell Observatory in the dark. by Christian Luginbuhl and Jeffrey Hall Partygoers and telescope hosts share a star-filled sky near Flagstaff, Arizona, during the city‘s annual star party. FLAGSTAFF DARK SKIES COALITION 54 ASTRONOMY • SEPTEMBER 2017 Venus sets among myriad stars above Flagstaff, Arizona, in this view of the sky from Buffalo Park, the site of the annual star party. FLAGSTAFF DARK SKIES COALITION FLAGSTAFF, ARIZONA, WRAPS picturesquely around the base of the San Francisco Peaks, the state’s highest mountain range. At an eleva- tion of 7,000 feet (2,130 meters), the air is thin, and nights are chilly even in summer. The bracing environment, however, doesn’t stop thousands of people from coming every September to Buffalo Park, a large open space right in the middle of the city, to peer into the cosmos. Here at the Flagstaff Star Party, rows of telescopes are hosted by the area’s many amateur astronomers, as well as by professionals from Flagstaff’s two major observatories: Lowell accessible viewing under unexpectedly Observatory and the United States Naval dark skies, within a 10-minute drive of res- Observatory (USNO). Despite the location taurants, hotels, and all the amenities of a less than 2 miles from City Hall, the sky is college town of 70,000 inhabitants. To the spectacular. The astronomers trace constel- quantitatively inclined, the event boasts lations and stars fainter than 6th magni- Bortle class 4 skies, a zenith sky brightness tude for the partygoers, and the autumn fainter than 21.2 magnitudes per square Milky Way rises from the looming peak of arcsecond, and a zenith limiting magni- Fnearby Elden Mountain, arcs through the tude of 6.5 or fainter. (The Bortle scale is a zenith, and dives into the southwestern nine-level scale of sky darkness created by “International Dark-Sky City” designation SENSIBLE DARK-SKY LIGHTING STANDARDS and nearly 80 percent of U.S. residents live horizon directly over the center of the city. astronomer John Bortle in 2001. Bortle 9 is by the International Dark-Sky Association where they can no longer see the Milky Even the splendid Sagittarius star clouds a terrible, urban sky, and Bortle 1 is a per- (IDA). Flagstaff shows in brilliant high- WOULD REDUCE SKY BRIGHTNESS OVER Way. Increases in the efficiency of lighting find little competition from the sky glow. fect sky with no terrestrial lights.) lights just what can be achieved. OUR CITIES BY 90 PERCENT OR MORE. technologies (most recently LEDs), always The Flagstaff Star Party bills itself as All of this stems from a 59-year tradi- touted as an opportunity to save energy, “The World’s Most Accessible Dark Sky tion of dark-sky preservation in Flagstaff, Preserving dark skies for leading into town. The natural night sky modern age, the problem has vastly acceler- have instead only contributed to the relent- Star Party,” a unique event providing easily which in 2001 was given the first astronomy — and more — as an environmental quality, as a ated, with an ever-increasing demand to less increases in the amount of light. Dark-sky protection in Flagstaff goes back resource to be enjoyed, as a tourism driver, use more light in more circumstances and How many of us know that this is not to 1958, when at the impetus of Lowell and as an ecological and health benefit — at more times. “The New World Atlas of necessary? and USNO astronomers, the city enacted is part of the ongoing conversations of resi- Artificial Night Sky Brightness” (available Sky glow impact Energy efficiency the world’s first law to protect night skies, dents, city planners, and advocacy groups online at http://advances.sciencemag.org/ Recovering the night (relative to LPS=1) (lumens/watt) banning advertising searchlights. Lowell like the Flagstaff Dark Skies Coalition. content/2/6/e1600377), published in the It doesn’t have to be this way. To examine (established in 1894) and USNO (1955) Decades ago, we all had to think con- June 2016 issue of Science Advances, the options, we return to our three-legged 10 100 steadily grew, and they now have over sciously about whether refuse went in the revealed in beautifully-colored maps the stool. 9 90 $125 million in telescope assets in the area. trash or the recycle bin; today it’s second un-beautiful consequences of increased Shielding. Use of fully shielded fixtures, LPS Preservation of the sky quality necessary nature. For a longtime resident of Flagstaff, artificial light: None of the land area in ensuring no light radiates above horizontal, 8 80 for astronomical research is contained in it’s startling to go to another city and not Europe or nearly anywhere east of the Great is simple and effective. Flagstaff does it; 6000K White LED Flagstaff’s lighting code and in its engi- see the Milky Way from downtown. Seeing Plains in the United States has naturally other dark-sky communities do it; anyone 7 70 neering standards. the galaxy and faint stars from the middle dark night skies; 60 percent of Europeans can do it. Even absent any other HPS At the heart of these standards is a pro- of a sizable town is second nature. 6 White 60 LED verbial three-legged stool for dark-sky pres- Unfortunately, it is also easy not to see 5 50 PCALED ervation: full shielding for outdoor them unless preserving the dark sky also fixtures, limits to the total amount of becomes second nature. Outdoor lighting spectra 4 40 installed lighting per acre, and spectrum 2000K LED6000K NBALED management calling for low-pressure Losing the night 3 30 sodium street and area lighting. The night sky has been a canvas of human HPS LED2000K PCALED Astronomy, however, is only part of the hopes and inspirations since we have been 2 20 equation. Flagstaff has built the idea of aware enough to raise our eyes from the PCALED Incandescent NBALED 1 LPS 10 looking up and seeing a star-filled sky into ground. Yet today, we find night’s window the city’s culture. You can find locals sip- closing almost everywhere, veiled by the HPS 0 0 ping a “dark-sky mocha” at Late for the spread of artificial light. NBALED The impact on sky glow from outdoor The energy efficiency of lighting varies Train Coffee, or unwinding at the end of Sensitive individuals noticed this inva- lights can be huge, as with white LEDs, widely, from the highly efficient (white the day at Dark Sky Brewing Company on sion long ago: In 1928, naturalist Henry LPS or minimal, as with low-pressure sodium LED and low-pressure sodium) to the less Beaver Street. A bit west of downtown, you Beston lamented, “With lights and ever (LPS) lamps or narrow-band amber (NBA) efficient (phosphor-converted amber and FLAGSTAFF DARK SKIES COALITION LEDs. Phosphor-convervted amber (PCA) narrow-band amber LED), to the woefully can turn off Flagstaff Ranch Road and onto more lights, we drive the holiness and Spectra of common outdoor lighting types show narrow emission from low-pressure sodium, at LED is in between. FLAGSTAFF DARK SKIES COALITION inefficient (incandescent). Dark Sky Lane. The IDA proclamation of beauty of night back to the forests and the bottom, which does little to interfere with night-sky viewing. On the other hand, broad spectrum FLAGSTAFF DARK SKIES COALITION dark-sky city status is found on signs sea” (The Outermost House). But in our LEDs, at top, emit light over a wide range of wavelengths, making them destructive to skywatching. 56 ASTRONOMY • SEPTEMBER 2017 WWW.ASTRONOMY.COM 57 The setting Big Dipper looms just over the horizon from the site of the Flagstaff Star Party, just 2 miles (3km) from the city center. Star-filled skies would shine over much more of the United States if effective lighting ordinances required better regulations, research shows that simply lighting. FLAGSTAFF DARK SKIES directing light to the ground where it is COALITION needed can reduce artificial sky glow by 50 Sky glow factors 100 percent or more. 90 25% Appropriate lighting levels. One can 80 find examples of excessive outdoor lighting 70 everywhere, but it can be managed with 60 50% practical limits on the amount of lighting. 50 Flagstaff’s code, for example, specifies any- 40 70% where from 25,000 to 100,000 lumens per 30 90% acre. Implementing these limits will reduce 20 sky glow by another 25 percent in typical brightness glow Sky 10 0 communities. Unregulated Shielding Total Spectrum. When you take a nighttime only Amount Spectrum flight, you can see the yellowish pinpoints only only of city lights going by below. Putting aside the point that if you’re seeing them at The amount of sky glow reduction one sees results from three factors: reasonable limits 36,000 feet, they’re not doing what they’re to the amount of light, good shielding, and supposed to be doing, the color, or spectral amber light sources. FLAGSTAFF DARK SKIES COALITION why they appear white — with dramati- THE INSPIRATION OF STAR-FILLED SKIES CAN During one September evening at the content, of the light is critical to light pol- cally greater emission in the blue and green Flagstaff Star Party, we overheard a pair of lution impacts. portions of the spectrum compared with RETURN TO MILLIONS OF OUR BACKYARDS IF visitors from Phoenix who had journeyed The yellow color arises from high- Improved energy efficiency is often touted yellow light sources like HPS.