BORTLE CLASS 8 / SKY KEY
City sky
Strong urban glow leaves mainly bright stars, planets and the Moon as easy naked-eye targets.
8
HOW TO READ IT
One number is a sketch of the sky, not the whole night.
A Bortle class describes what the sky looks like under particular conditions. Walk across a large park, turn toward a town, add snow or smoke, and the view can change. Use the number to compare darkness quickly, then read the stop page for the horizon, headlights, access and everything else that decides whether the place actually works.