Scientific Metrics
Sky Quality Meter (SQM)
An instrumented reading that measures the brightness of the night sky in magnitudes per square arcsecond.
A Sky Quality Meter (SQM) is a handheld or mounted device that provides a precise, numeric reading of sky brightness.
Magnitudes per Square Arcsecond (mag/arcsec²)
SQM readings are typically expressed in magnitudes per square arcsecond. In this scale:
- Higher numbers mean a darker sky.
- 22.0: The theoretical limit of a perfectly dark sky.
- 21.0: Excellent rural dark sky.
- 19.0: Typical suburban sky.
- 17.0: Bright urban sky.
Unlike the Bortle scale, which is somewhat subjective and based on visual observation, SQM provides an objective, scientific measurement that can be tracked over time to measure the impact of local light pollution.