Shedding Light on a Common Problem

Posted on Wed, January 18, 2012

If you've been to any of the nighttime observing sessions at our Public Observatory, you might have wondered why we mostly view the planets and the Moon. After all, the Observatory houses a professional 16-inch telescope, and several other high-quality portable telescopes; shouldn't they be able to show us great views of galaxies or nebulas?   They should, and they could, if they were located at what astronomers call a "dark site" — away from the city lights that often outshine the lovely stars of nighttime.


Public Observatory

The Observatory at night. Photo credit: National Air and Space Museum, Eric Long


The problem is light pollution. The International Dark-Sky Association (IDA) defines light pollution as "any adverse effect of manmade light." This includes but isn't limited to our disappearing view of the Milky Way and the difficulties astronomers experience in making observations of celestial objects. Living things experience many effects as well: nocturnal animal populations are shrinking as they have difficulty finding food and hiding from predators, sea turtle hatchlings can have trouble finding their way to the ocean and die, and migrating birds can be disoriented by lights. Emerging research on the effects on humans indicates several problems associated with disruption of circadian rhythms and melatonin production, not to mention the safety-related dangers that come with poor visibility at night caused by glaring lights. But there are easy solutions: shielding lights to reduce glare, dimming lights to provide the right amount of light, and turning off lights when they're not needed.



Potential intruder hides in the glare from a “security light.” Photo credit: George Fleenor


When we decided to build the Observatory as a place for the public to gather and do astronomy together, we knew that light pollution would be an issue for us. But in order for it to be a convenient gathering place that people could get to easily, we knew we needed to build it in the city, where the people are. It was an easy decision when we considered what we were trying to do, and so far more than 2,000 visitors have enjoyed our nighttime observing sessions. And yet we and our visitors long for darker skies and the ability to view fainter stars, galaxies, nebulas. Wouldn't it be wonderful to be able to look at the majestic arms of the Milky Way from Washington, DC? It won't happen for us until we have more intelligent and efficient street lighting here in our nation's capitol and in the surrounding area. One way to work toward this is to collect scientific data that can be shared with decision makers to demonstrate what our current situation is regarding light pollution, how it's been changing, and its effects. Since 2006, citizen scientists from around the world have been participating in a program called GLOBE at Night. It's a worldwide attempt to measure light pollution and see how it varies from place to place and year to year. This year, there are four opportunities to participate: January 14-23 (right now!), February 12-21, March 13-22, and April 11-20. The dates are selected so that the Moon won't be up in the sky when participants are making observations, because the Moon also brightens the sky and can outshine the stars, especially when it's near a full moon.


The constellation Orion, as it appears under magnitude 2 (left) and magnitude 4 (right) skies. Photo credit: GLOBE at Night/NOAO


Want to join in? Here's how it works: Go outside an hour or more after sunset and give your eyes a chance to adjust to the darkness. Find the constellation Orion by looking in the southern sky. GLOBE at Night provides magnitude charts that show what Orion looks like with different amounts of light pollution. Magnitude refers to how bright the stars are, and when you’re talking about light pollution, it describes the faintest stars that can be seen. Determine which magnitude chart looks most like what you see that night and report it online. The reports show up instantly on GLOBE at Night's interactive map viewer, so you can compare what you see to what people in different places around the world see. On Saturday night, January 14, I reported magnitude 3 skies from the Public Observatory in Washington, DC, and I’d love to know what your skies are like!



The waxing gibbous Moon as we viewed it on December 3, 2011. Photo credit: National Air and Space Museum, Genevieve de Messieres


For now, we mostly stick to visually observing the planets from the Observatory’s perch at the National Air and Space Museum. These objects are bright enough and big enough to observe easily even under light polluted skies, and they aren’t especially sensitive to the unstable air in our area which blurs high-powered views. The Moon fascinates me every time I see it, even when I see it every day. I enjoy observing the planets and looking for subtle changes and details I never noticed before, and I think that many of our visitors wouldn't disagree. And this past Saturday night, I delighted in a great view of the Orion Nebula, a star-forming region, through our telescopes. But I am hopeful for a future in which we can use our fantastic telescopes to see more of the farther, fainter wonders of our universe from the National Mall in Washington, DC. Katie Nagy is an astronomy educator at the National Air and Space Museum in Washington, DC.

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