Flagstaff mandates that shielding be placed on outdoor lighting so that it doesn’t project skyward. There are also limits on the lumens of light allowed per acre of land.
The result is a starry sky visible even from the heart of the city. Flagstaff’s Buffalo Park, just a couple miles from downtown, measures about a 4 on the Bortle scale, which quantifies the level of light pollution. (The scale goes from 1, the darkest skies possible, to 9, similar to the light-polluted night sky of, say, New York City. To see the Milky Way, the sky must be below a 5.)