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Light pollution over El Cajon, CA: how dark is the sky?

City lights glow up into the sky for up to 100 km. Tap the map or use your location: we add up every light around it from NASA's satellite picture and tell you what the night sky looks like there.

El Cajon, CA

Adding up the lights around this spot…

Or tap anywhere on the map.

🌌 Nearest darker sky

No clearly darker sky within 150 km. Head for high ground with the lights at your back.

How we work it out

  • Satellite lights

    NASA's VIIRS satellite photographs the Earth at night: every lit town shows up.

  • 100 km around

    Each light is added in, weaker the farther it is (falling with distance to the power 2.5, as sky glow does).

  • Bortle class

    The total becomes the 1–9 Bortle class astronomers use, checked against dark-sky parks and city centres.

Lights from NASA's 2012 cloud-free night-lights composite (the one our classes are calibrated on): towns that have grown since may be brighter. An estimate, not a meter reading. Images: NASA Earth Observatory / GIBS

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