Exceptional aurora borealis of 10-11 May 2024 observed by alpine cameras

The Sun has a cycle of activity with a maximum every eleven years, characterized by flares of hot plasma, emissive in X-rays, and ejections of ionized material that can sometimes propagate to the Earth by following the lines of the interplanetary magnetic field from the Sun (under certain conditions of initial directivity). The activity of May 2024 reminds us that we have reached the solar maximum of cycle 25 (2020-2031). Although not rare in terms of the energy of the X-rays detected, the flares observed by astronomers nevertheless gave rise to a truly remarkable geomagnetic event, in the TOP 10 of the most intense phenomena since 1950. Thus, coronal mass ejections from the solar active region NOAA 13664 impacted the Earth, causing large-scale aurora borealis on the night of May 10 to 11, clearly visible in France as far as the Côte d'Azur. They were recorded by the high-quality automatic and panoramic alpine cameras (cameras with a large sensor sensitive in low light) that have recently been installed in some resorts. Although their purpose is quite different (tourism, meteorological and snow monitoring), their presence constitutes a new tool for documenting rare phenomena in our latitudes, making them useful for night surveillance of the sky (auroras, comets) over 360° in the vicinity of the horizon. Here we present some of the best shots and animations at low frame rates (10 to 30 minutes) from these cameras. The celestial spectrum obtained in Antibes by Christian Buil and the Star'Ex amateur spectrograph makes it possible to identify the excited atoms in the upper atmosphere (nitrogen and oxygen lines) at the origin of the observed colours.