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About the data
Overlay shows artificial zenith brightness from David Lorenz's 2024
atlas, derived from VIIRS satellite data. LP Zone, LP Index (ratio
of artificial to natural sky brightness) and mag/arcsec² are read
from the same binary grid the official viewer uses, at 1/120° (~1
km) resolution.
Note: this is zenith brightness, not the
Bortle scale,
which is a subjective whole-sky metric and not directly comparable.