What is the Bortle scale?

A 9-level scale of night sky darkness, from Bortle 1 (pristine wilderness) to Bortle 9 (inner city). The map color-codes Bortle class by location.

How do I find a dark sky near me?

Zoom out on the light pollution map and look for Bortle 3 or darker zones within driving distance. Hills and open fields work best.

A lot. Light pollution erases the Milky Way, faint stars, and most deep-sky objects. Darker skies reveal hundreds of times more.

Understand your sky quality using the Bortle Dark-Sky Scale

Data Year:

Overlay Opacity:

50%

Search location:

Bortle Scale

1 Excellent

2 Dark

3 Rural

4 Rural/Sub.

5 Suburban

6 Bright Sub.

7 Sub./Urban

8 City

9 Inner City

Light pollution data: David Lorenz Light Pollution Atlas using NASA VIIRS satellite imagery. Map tiles: OpenStreetMap contributors.

John Bortle's nine-level scale rates the darkness of an observing site, from pristine dark skies to inner-city glow.

Select your Bortle class to see what objects and phenomena are visible.

Your Bortle Class: