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Since 2016, scientific instruments placed at the summit of mount Mégantic have been observing the changes in the night-sky luminosity. These tools allow us to keep watch on the quality of the starry sky in the core of the Reserve. In order to better follow the evolution of light pollution, measurements are now also taken from the city of Sherbrooke.

Measuring artificial light

By measuring the luminosity at the zenith, i.e. the highest point in the sky, it is possible to record the amount of light coming from natural and man-made sources every minute of the night. Depending on the proximity of cities and the level of light pollution, we can therefore follow the changes of the latter during the night or see its evolution over the years.


On the other hand, when the level of light pollution is very low, then the luminosity values depend above all on natural sources such as the stars, the Moon, the Milky Way and luminous phenomena such as the "airglow" and the northern lights. This is the case at Mont Mégantic, where light pollution occurs mainly in the form of light domes above the horizon and is therefore practically zero at the zenith. The luminosity values recorded throughout the year therefore vary essentially according to the lunar cycles and the position of the Milky Way in the sky.

An analysis of the measurements made by the various instruments is available in our annual report.



The Sky Quality Meter (SQM) is an instrument designed to measure the luminosity of the sky continuously. Developed in Canada, it is used widely around the world by both professional and amateur astronomers, due to its simplicity and efficiency.


While a handheld model exists and is often used in field-surveys, the SQM installed on the summit of mount Mégantic is automated and works continuously to record brightness of the night sky.



Another SQM-like instrument, named TESS, has been installed in parallel since 2019. The advantages of the TESS are its ease of installation, its infrared sensor for estimating cloud cover, and its live broadcast of the recorded data. This instrument is an initiative of the European STARS4ALL project and the data of all TESS deployed around the world is openly available.  


The spectral range of the TESS is slightly different from SQM, so the measured values are not directly comparable between these two devices. On the other hand, this second photometer makes it possible to validate the results obtained with the SQM and the redundancy makes it possible to ensure continuous monitoring in the event of prolonged failure of one of the instruments.

A few years ago, another TESS was also installed at Mont Bellevue, in Sherbrooke. By being positioned in a place where the amount of artificial light is higher, it is easier to measure and follow the evolution of artificial llight in the city over the years.

Mont Mégantic - stars657

Sherbrooke - stars781


An ultra-sensitive "all-sky" camera is installed near the Mont-Mégantic Observatory and continuously photograph the entire sky. It not only allows the Observatory to keep an eye on atmospheric conditions during astronomical observations, but also to photograph the different sources of artificial light on every night. It is also equipped with Johnson filters, so that we can measure light pollution in multiple colours and see its evolution over time.


The last image captured by the camera can be seen below:

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