The Bortle Scale: A Flow Chart

The Bortle Scale is a useful way of estimating your sky brightness, i.e. to what extent light pollution affects your view of the night sky. By going outside on a clear moonless night and recording what astronomical objects you can see you can assign a Bortle Class rating to your observing site.

I have used the Bortle Scale to assess night sky quality many times, and always felt the lack of a handy flow chart to lead me through it. So I made one. Enjoy. (You can also download the pdf version.)

PS The content of this chart assumes some prior knowledge of astronomy, but any of the terms used are easily google-able.

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