The Bortle scale measures sky darkness from 1 (darkest) to 9 (brightest).
THE SKY WILL ANSWER
BORTLE / SKY
A 1–9 scale for how dark the night sky looks.
THE MILKY WAY IS SOFTLY VISIBLE.
BORTLE DESCRIBES SKY BRIGHTNESS — NOT CLOUDS OR WEATHER.
Overhead reads a compact, downsampled version of the Falchi et al. World Atlas raster in your browser. It converts modeled artificial zenith brightness into an approximate Bortle class for a clear, moonless night.
Bortle classes describe visual conditions, so weather, nearby lamps, altitude, the Moon, and your eyesight can make a real night look different. The sky render is an illustrative zenith view, not a live planetarium.