How dark does it need to be?

What sky glow does

Artificial light scatters in the atmosphere and brightens the sky, especially towards the horizon — exactly where the aurora first appears when you are away from the pole. Snow cover makes it worse by reflecting light upwards.

How we estimate it

For each place we add up night-time light measured by NASA's VIIRS satellite instrument within 50 km, weighting nearby sources more strongly, and group the result into six classes from pristine to city sky. Where it helps, we also point to the nearest area with clearly less light.

Finding a good spot

• Put the brightest town lights behind you, facing the direction of the aurora.
• Lakes, beaches and open fields give an unobstructed horizon.
• Even a 10–20 minute drive often moves you from suburban to rural sky.
• Check access and parking in daylight if you can.

Your eyes matter too

Dark adaptation takes 20–30 minutes and is lost in seconds by looking at a bright screen. Use red light, dim your phone, or switch on the red night-vision mode of this site.