I live in a city. I can see pinpricks of bright stars, but I miss the spill of the Milky Way. Cities don't need to be this bright, and dark skies don't need to be a distant memory from trips to deserts, mountain tops, and vacations far from home.

Explore how bright your city is at night with an interactive map. Image credit NASA.

My city is not the worst offender of urban light pollution, but like most cities, it not friendly to stargazers. The attitude of light, light, and more light is so endemic to human habitation that the Bortle Scale for light pollution names all but the two darkest classes after settlement population density.

Light pollution comparisons using the Bortle Scale. Screenshot from the Stellarium.


The building I live in has a pair of spotlights so bright I can read by them at night from over 100 feet up. When I objected to their installation (and then to an upgrade for higher-wattage bulbs), I was informed that lighting up the sides of slick-sided high rise was essential for security. Apparently, Spider-Man is real, a supervillain, and coming for my potted plants, but don't worry because he's also photophobic!

The particular ridiculousness of my building's illumination issues is unique to them, but this kind of wanton lighting pollution is based on the fallacy that brighter is safer. When that brightness floods out and up, the glare actually reduces safety by blinding drivers or pedestrians, increasing contrast to create blind-spots in dark shadows, and adding visual distraction. Shielded lights direct light down to only where it's needed, increasing visibility without lighting up the dark skies.


Lighting fixtures rated by dark-sky friendliness. Image credit University of Florida.

What can you do to bring dark skies to your home? Switch lighting fixtures. Lighting 90 degrees from the ground is all glare that blinds you, so shelter bulbs to direct the light at the ground where you can actually use it. This limits how much energy you spend on lighting up areas you aren't using (and don't even want to light), limits light trespass into nearby buildings, and makes your skies more friendly to stargazers. For bonus points, limit how many hours a day the lights are on (does the sign on an 8am-6pm hardware store really need to be lit up in all its glory at 3am?), or set them up on motion sensors to only flip on when needed.


Once you've taken care of your own home, you can campaign your city for bylaws on appropriate outdoor lighting. As a reward, you'll recapture the beauty of the night sky, and maybe, just maybe, see why our galaxy is called the Milky Way.

Night-sky composite photograph in Ontario, Canada by Kerry-Ann Lecky Hepburn

Head to the Earth Observatory to learn more about urban light pollution, or to the International Dark Sky Association for resources on how to make your home more dark-sky friendly. We'll be talking about cities that have made the change to Dark Sky Parks next week on the Space subsite.