Why this exists

Searching "how dark is the sky where I live" mostly turns up a paid interactive map or a Bortle-scale explainer with no number attached to your own town. DarkSkyCheck instead reports one plain figure per city, worked from a public satellite dataset, plus the one thing a lookup alone can't tell you: how far away a meaningfully darker sky actually is.

What goes into the number

Every city's figure comes from NOAA and the Colorado School of Mines Earth Observation Group's VIIRS Day/Night Band annual composite for 2025, sampled as the median of a 3x3 pixel window (roughly 1.4km) centred on the city, so one lit car park or intersection doesn't skew the whole town. City boundaries, coordinates and population come from the Census Bureau. The exact bands and the honesty caveat behind them are documented in the methodology guide.

Satellite radiance, not a Bortle rating

This is the one thing every page repeats on purpose: a satellite measures light radiating up from a city at night, a Bortle rating is a person's eyes on the ground. The two agree often enough to be useful and diverge often enough to matter, covered fully in the Bortle scale guide.

Who runs this

DarkSkyCheck is an independently run site, not affiliated with NOAA, the Colorado School of Mines, or DarkSky International. Each city's page is generated directly from the public dataset above rather than written freehand per city, then checked against that same source data before publishing, the way a spreadsheet is checked against its formula, not invented editorial. Where a page ever carries a sponsored or affiliate link, that will be disclosed on the page itself and in the privacy policy.