During the nights of December 2 and 3, 2016, images were taken from the Pic du Midi de Bigorre observatory to assess the light pollution halos over approximately 270° of azimuth from north to west, passing through the east and south.

The image above shows the horizon over a hundred degrees of azimuth centered on the northeast. In this 1-minute exposure, taken with an 8 mm lens and a 2.4 aperture (ISO 800), we are struck by the multiplicity of halos and the great distances at which they are visible. We can see the predominant influence of the Toulouse and Tarbes halos. On this image, the main halos are marked with their respective source distances [click on image to enlarge].

The map below shows the directions of the various halos present on the image. Perpigan is more than 220 km from the Pic du Midi and its halo is clearly visible to the east.

SQM measurements were carried out on both nights and consistently delivered values between 21.1 and 21.2 mag/arcsec2 , using a single instrument. The Moon was not present. To the eye, the sky gave the impression of being between classes 3 and 4 on the Bortle scale, with the Milky Way fairly visible but lacking in detail and fading towards the horizon. Ground-based equipment was clearly visible.

The two images below show similar shots taken in the south-east and south-west directions with their main halos spotted.

Note the negative influence of the nearby La Mongie ski resort. Over the last 20 years, the southern horizon of the Pic du Midi has gradually seen halos of light pollution develop, and it is no longer possible to enjoy a truly black sky all the way to the horizon (which affects the visibility of the Sagittarius and Scorpio constellations in summer, for example). On the western side, the halos of Saint-Sébastien, Saint-Jean-de-Luz, Biarritz and Bayonne strongly illuminate the horizon in this direction. The points of light in the mountains in these two images are the headlights of the snow groomers preparing the slopes at various ski resorts.

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