The Bortle Scale
The Bortle Scale is a nine-level classification system used to describe how much light pollution affects the night sky.
A lower Bortle rating means darker skies, greater visibility of stars, clearer views of the Milky Way and better conditions for observing deep-sky objects.
Excellent
Bortle 1–2
Rural
Bortle 3–4
Urban
Bortle 7–9
Many of the UK's best stargazing locations are found between Bortle 2 and Bortle 3, including official Dark Sky Parks and remote rural areas.
Sky Quality Meter (SQM)
SQM readings measure the brightness of the night sky in magnitudes per square arcsecond.
Unlike the Bortle Scale, which is based on observation and classification, SQM provides a numerical measurement of sky darkness.
A reading around 21.5+ is considered excellent for astronomy and usually indicates a location where the Milky Way can be clearly visible on a suitable night.
Beyond Measurements
Numbers only tell part of the story.
We also consider practical factors that affect how enjoyable a night beneath the stars will be:
- Open horizons and visibility of the sky
- Nearby artificial lighting
- Privacy and surrounding buildings
- Whether guests can comfortably enjoy the sky from the accommodation