Light pollution - Pollution lumineuse : cartographie globe terrestre

Publié le 2 Décembre 2020

Light pollution - Pollution lumineuse : cartographie globe terrestre

If you have never seen a clear, starry sky from a place devoid of light pollution then you don’t know what you’re missing.

With the naked eye alone from a dark site you’ll see thousands of stars, meteors, the zodiacal light, airglow, satellites, the milky way, nebulas, and occasionally auroras and comets. Check out the Photography page to get an idea. If you bring a telescope or even binoculars you’ll see more detail than you could ever expect to see from a city. I created this website for those who are interested in finding a dark place to observe the night sky or capture the heavens. In the past finding a dark sky was easy: just drive a few miles outside of town. But with increasing light pollution, even driving 50 miles away from a major city isn’t enough to clearly see the stars. Finding a pristine sky is not as easy as it once was. But you can use the Map on this site to help you.

Tip: Before looking for a dark site, consider what it is you want to see. For many people getting to a 100% dark sky is not possible without spending an entire day driving. But if you look for a site where the sky is only dark in the direction you want to observe, it becomes easier. For example if you want to see the core of the milky way galaxy, look for a place that is dark to the south with no major cities in that direction.

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Keep in mind that the light pollution data in these maps is from 2006 and may have changed slightly.

Also check to see if the moon phase is favorable before heading out to darker skies


What does the color scale on the light pollution map actually mean?

There are 15 colors found on the map. Some have tried to tie it into the Bortle Scale or into specific SQM readings. But I’ve purposely avoided defining the color scale. This is for several reasons:

  1. The map doesn’t take weather into account. Humidity in particular has a big effect. When there’s a lot of moisture in the air it tends to scatter the skyglow over greater distances. Whereas air with low moisture content can yield darker skies even close to a town. All else being equal, the same color zone will be darker in a dry climate compared to a humid one. Smoke and air pollution also have an effect.
  2. The map doesn’t take elevation or terrain into account. An observing site on a mountain top will often have a much clearer sky because you’re above a lot of the haze and air pollution in the lower atmosphere. A high vantage point lets you see stars all the way down to the horizon and puts you above a lot of the light domes. But because you can see so far there may still be plenty of lights in the distance. When you observe from a valley, a hill or mountain may block the light dome from the nearest town. Of course the stars in that direction will also be blocked, but this can make the sky seem a lot darker.
  3. The map doesn’t take very localized lights into account. You might think you’ve found the perfect observing site by looking at the map. But when you visit at night you find out there’s a new oil drilling rig or a bright security light on the nearest farm house.
  4. Light pollution is not uniform across the sky. It will always be brightest in the direction of the nearest city. Consider what it is you want to observe and find a site that’s darkest in that direction. Most of the time, having a dark sky to the south is most important for seeing the milky way. But for seeing the aurora borealis, you want a dark sky to the north. For viewing planets or the moon, light pollution is not a concern, you just want to get away from the glare of nearby lights.

The light pollution map is really just an estimate to help you find the best place near you to see the stars. But sites within the same color zone can have very different levels of light pollution. The only way to know for sure how dark a viewing location is, is to go there at night. Or you can visit a dark site submitted by other stargazers to be a little more certain of what to expect.

So what color zone should you seek out to find the best views of the stars? The short answer is to visit a black or gray zone. But for a lot of people that’s not practical as it’s simply too far away. I would recommend at least a green zone to get a taste of what a truly dark sky can offer.












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