Sky Quality Meter (SQM)

Sky Quality Meter (SQM) from Unihedron: Measure the Quality of the Night Sky

The Sky Quality Meter (SQM) from Unihedron is a highly accurate measuring device designed to assess the brightness of the night sky. This key indicator of light pollution is highly prized by amateur astronomers and astrophotographers, enabling them to quantify the quality of observation sites. Made in Canada, the SQM is an essential tool for any study of light pollution.

Operation and Main Features

• Measuring principle : The SQM uses a sensor sensitive to visible light to measure sky brightness in magnitudes per square arcsecond (mag/arcsec²). This logarithmic scale makes it possible to evaluate the "brightness of the sky background" over a square observation area of one arcsecond on a side. Measured values range from 16 (very bright sky) to 23 (extremely dark sky).
• How to use : The device should be pointed towards the zenith, in an area free of obstacles (trees, mountains) or extraneous light (street lamps, Moon, Milky Way). Once activated, it displays the results on an LCD screen after a few seconds.
• Measuring time : Very fast, especially in polluted areas (a few seconds), it can take up to 80 seconds in the darkest places.

Available models

• Classic SQM : Wide measurement angle, suitable for general observations.
• SQM-L : Version with integrated lens for a narrower field of view, offering more precise measurements for specific areas.
• SQM-LE and SQM-LU : Connected versions for continuous monitoring via USB or Ethernet.

Applications

SQM is used for :

• Compare sky quality at different sites.
• Document the evolution of light pollution.
• Plan optimal astronomical observations.
• Calibrate qualitative scales such as the Bortle scale.

Summary

The Sky Quality Meter is a compact, precise and indispensable tool for anyone wishing to objectively analyze the quality of the night sky. Whether you're an amateur astronomer or a professional, the SQM is an invaluable ally for studying light pollution and optimizing your observing conditions.