Citizen Scientists Measure Bright Skies
For Hilo, HI, sky brightness measurements by citizen-scientists show a gradient from bright-to-dark as one moves from the city center to outlying areas.
Credit: C. Peruta, C. E. Walker and NOAO/AURA/NSF

Astronomy is about photons: collecting and analyzing photons of all energies reveals the universe. When the professional astronomy community assembles, as it has here in Hawaii, there's a high density of photon hunters. Ironically, the stars are hardly visible outside our hotels. Like other high-rise cities, Honolulu floods the night sky with light. Worldwide, many people live in urban and suburban centers under light polluted skies where the stars are barely visible.

Earlier this year in March, a globe spanning star party invited people to measure the light pollution in their neighborhood skies as a part of "Globe at Night." Here at the AAS meeting, a team of astronomers and educators from the National Optical Astronomy Observatory reported on the preliminary data from the 2007 campaign. So far, the 2007 Globe at Night campaign has logged almost double the number of measurements at the 2006 campaign. It's an expanding project that engages the public in collecting valuable data.

The idea of citizen scientists counting the stars at night to assess light pollution originated with campaigns in Greece and Austria. In 2006, several US organizations collaborated to initiate a US-based naked-eye star counting with "Globe at Night". The standard, or classic program is to observe the constellation Orion, and compare your sky with a set of star maps representing different levels of light pollution. It's simple, produces reliable data, and engages people in many places. This year, US reports were received from 49 of 50 states.

For 2007, NOAO expanded the observing program with the addition of handheld digital sky-brightness meters to measure sky glow, a.k.a., light pollution. Stephen Pompea, an astronomer and manager of science education at NOAO said, "The classic version is clearly gaining momentum. The digital mode, using sky-brightness meters procured and distributed with special funding support from the National Science Foundation, came together just in time and the early results from this prototype project show great promise."

The new, digital meters were shipped to teachers and students, amateur astronomers, science centers and museums, and observatories in the US, Mexico, Chile?where NOAO operates and observatory?to collect and report measurements. More than 800 sets of digital data have been submitted, and the team anticipates further reports. Sample city maps of selected locales include Tucson, the home of NOAO, Washington DC, Richmond VA, Sonora Mexico, the island of Hawai'i and Las Vegas.

Connie Walker, an astronomer and senior educator at NOAO, is lead coordinator for Globe at Night. She explained "These initial maps are only a first look, but the data show signs of good consistency and a gradient of bright to dark measurements as one moves from the city center to outlying areas." Ultimately, this sort of data can provide ground truth to satellite-based measurements of night sky light pollution.

With a smile, Walker explained that people were very creative in the data collection strategies. Teams of students took multiple measurements at the same site, and averaged the data to submit it to Walker. In other cases, GPS-equipped teams drove about their hometowns, shot the sky through the "moon roofs" of their cars, and recorded the data with corresponding GPS position. Most all of the 135 teams making digital sky brightness measurements are now proposing an extended set of year-round measurements. Observations through the night could record the changing patterns of night lighting levels, or seasonal lighting changes that depend upon sports arenas and other urban activities. There's also the possibility of discovering dark sky oases amidst the light polluted skies, and obtaining the observations that can be used to defend these dark spaces.

Walker looks forward to working with the teams collecting digital data, and to expanding the program to include more people and locations as we approach 2009, the International Year of Astronomy (IYA). She's the US Chairperson for the Dark Skies Working Group for IYA, and sees the 2007 campaign as a successful model for creating a worldwide network of citizen scientists using both their eyes and simple light meters to assess light pollution.

At a time when we're all becoming conscious of the conspicuous consumption of energy, assessing our light polluted skies is a first step toward better energy management. And, as both an educator and photon hunter, I truly hope it is also a step toward darker skies. It's not simply about better conditions for astronomical observations; rather, it's about restoring the beauty of the night sky for everyone.