Globe At Night: Measuring Light Pollution with Human Eyes

Mark your calendars for March 16 through 28. Don't ask why, yet. Now, read on....

Composite image showing centers of urban light emission
Credit: NASAWant a chance to do some "citizen" science, contribute to an international investigation, and have some fun to boot? An opportunity is coming up in March: Globe At Night. All you need is your eyes....

The problem is summed up in two words: light pollution. A good deal of light produced by human civilization--streetlights, porch lights, shopping malls, security lighting, night time work lights, store fronts, parking lot lights, billboards, neon signs, the list is lengthy--shines or reflects upward into the atmosphere, there scattering off of suspended particles, like dust grains, water droplets, ice crystals and the like.

The scattered light shines back down from the sky, and we see it as a dull nocturnal glow, sometime faint, and sometimes quite pronounced. The amount of scattering particles in the air has an effect on the brightness of the night sky, but the root of the matter is the amount of light sources whose light escapes upward. The closer you are to the heart of an urban area, the more light pollution you will be subjected to.

So what? What's so harmful about that sky glow? Sometimes it can even look kind of pretty....

Well, the fact is, if you've never seen a clear night sky far from sources of major light pollution, you may not appreciate what you're missing: the sight of a clear and dark night sky in which you can literally see thousands of stars. And if you have seen a pristinely dark night sky before, think about the fact that, in 2008, half the population of the Earth was living in cities, many of whom may never have been out of their urban worlds, and for whom the night sky is naturally a dull version of day with a handful of washed out stars above.

There are also effects of light pollution on wildlife that include disturbance of day/night sleep cycles, less cover of darkness from predators, and even effects on plant life.

Globe At Night is a program that's been going on for a few years now whose aim is to measure and monitor the varying levels of light pollution around the world by using individual people as the instruments of measurement.

And it's pretty simple to participate in. The idea is that the brighter the light pollution is in any given location, the few stars you can see. The faintest stars quickly become drowned out in the sky glow, leaving only the brighter ones for your eyes to pick out. All you have to do is go outside on one or more nights in the last half of March, find the constellation Orion (which is pretty easy to find, even in a city), and count the number of stars you see there. Then, report your count through the Globe At Night website, where you'll also be able to see the observations of everyone else around the world, as well as find full instructions for participating.

Now, calendars marked? Know where Orion is? Have a sweater handy? You're all set....

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