I remember the first time I saw a truly dark sky.
My parents had sent 12-year-old me to a summer camp in the mountains of central Virginia. I’d grown up in the Washington, D.C., suburbs, where houses and streetlights illuminated the night sky, so it was rare to see more than a couple of hundred stars at any one time.
At that rural camp, though, the situation was very different. One night the camp’s counselors drove us out to a nearby field. We leapt from the truck, and when its headlights went dark, most of us started horsing around—but not me.
I stood motionless, head tilted up and jaw hanging slack, transfixed by the view of the sky.
There seemed to be millions of stars overhead, far more than I had ever dreamed. The Milky Way seemed bright enough to cast shadows, and I was lost, unable to find any recognizable constellation in the stellar swarm above. I was no neophyte—I had a telescope at home and knew my way around the sky—but the stars were on cosmic overload.
It was awesome, in the true meaning of the word, and I will never, ever forget how I felt in that moment.
Chances are, however, if you go outside on some clear, moonless night, your view won’t be quite as spectacular. More than 80 percent of humanity is affected by light pollution—light that is wastefully cast up into the sky and washes out the stars—and for those in the U.S. the statistic is much higher, approaching an astronomy-busting 99 percent.
The fading of the stars is a matter of contrast. With so much light going upwards, away from where it’s needed on the ground, the air in our atmosphere and particles called aerosols suspended within it scatter and reflect that light back down to us. We see the sky itself as a source of light. Stars are faint and have to compete against that glow. If the sky is too bright the stars cannot win, and our eyes cannot pick them out among the blazing soup above.
This is one of the major reasons why astronomers build their observatories away from city lights in difficult-to-reach locales such as mountaintops in Chile, Hawaii and Australia. So far removed from the lights of humanity, the light from the stars is easier to see.
Professional astronomers measure the night sky’s brightness in a complicated way, but the gist is that they count how many noncosmic photons they see coming from a small patch of sky. This is useful for quantitatively comparing one observing site with another, but it’s not ideal for the average person who just wants to know where to go to see the heavens as clearly as possible. There’s also an inescapably qualitative aspect of gauging darkness because some people can see fainter celestial objects than others. Astronomers capture some of this subjectivity in a concept called “limiting magnitude,” where the limit is the brightness of the faintest star you can see. (Astronomers measure brightness in a system called magnitudes.)
In the February 2001 issue of Sky & Telescope magazine, amateur astronomer John Bortle presented a hybrid plan that uses both quantitative and qualitative measures to create nine levels of sky brightness. Now known as the Bortle scale, many amateur astronomers use it, and it’s handy. A Bortle 9 site, such as the middle of New York City, has the worst light pollution, and even the brightest stars overhead can be difficult to spot. From there the levels correspond to what you can see from a smaller city, the urban-to-suburban transition, the suburbs and then rural and even darker skies. The scale is a bit arbitrary, but that’s okay; it’s meant to give easy estimates for the view from a given spot, not precise measurements.
Bortle 1 sites are rare, but they do exist in the U.S. You can see how your own location ranks using an interactive light-pollution map. It’s a useful tool if you want to find a good spot for stargazing or watching a meteor shower—the wonderful Geminids peak on December 14, 2023, for example.
Where I live in central Virginia (not all that far from where I camped all those years ago), the sky is right around a Bortle 3. That’s not perfect, but it’s still so dark that even seasoned observers can be surprised: while outside one recent night, I saw the Pleiades through the trees and could scarcely believe how bright they were, even compared with where I used to live in semirural Colorado. Dark skies make a huge difference.
DarkSky International is an advocacy group that aims to restore the skies to their pristine darkness as much as possible. It does this by promoting the use of better nighttime illumination, for example. It also certifies dark sites around the planet, ones that have “responsible lighting policies and public education,” and curates a searchable list of certified locations. Some of those sites offer cabins or other accommodations where you can stay and maximize your celestial enjoyment, too.
In fact, astrotourism—taking vacations to dark sky destinations for stargazing—is an increasingly popular phenomenon. Many companies offer travel packages to places around the world where you can take in the sights by day and spend your nights under the heavens. There’s even an independent website that connects with an online booking company to give prices for various hotels overlaid on a light pollution map if you want to try your own hand at it.
I’ve visited many dark sites in the decades since that unforgettably spectacular evening at camp when I was young—some where the sky was even darker and the stars were even more plentiful. And every time—every single time—the experience is just as jaw-dropping and magnificent. When I stand under the star-filled sky, I’m still that 12-year-old boy seeing it for the very first time. No matter how much time passes, that feeling never gets old.
We’re in danger of losing all this to light pollution. If you can, find a dark site, spend a night taking in the universe, and then take a look at the DarkSky International page and see what you can do to help reduce light pollution. Everyone deserves the stars.
