AIRGLOW at ORM (La Palma)

At 2400 meters, high above the sea of clouds, in the most vertical island in the world (La Palma, Canary Islands), in the Atlantic Ocean, we find the Roque de Los Muchachos Observatory (ORM), a privileged place to observe the Universe. Thanks to the special atmospheric conditions and low light pollution, the sky from the top of La Palma is exceptionally dark. This is where the Gran Telescopio Canarias (GTC), the largest optical-infrared telescope in the world, is installed. During the night of May 27, 2014 we observed a rare atmospheric phenomenon: an "Airglow" (green luminescence in the sky). Virtually invisible to the naked eye, this type of light becomes perceptible anywhere in the world (unlike the auroras, which only occur at high latitudes), provided that the quality and dark sky allow.

This time-lapse video shows different sequences in which the "Airglow" is clearly identifiable. Made with a DSR (Digital Single-lens Reflex) camera and 40 seconds exposure, we can see about 20 minutes of real time in each second of the video. The characteristic luminescence is produced by the recombination of various atoms (mainly nitrogen with oxygen or hydrogen, but also sodium or iodine) in the upper atmosphere (about 100 km altitude), after being ionized by ultraviolet sunlight during the day. The Airglow is normally visible near the horizon –being extremely weak, that is where, due to perspective, our vision sees through a greater amount of atmosphere, making the brightness more evident. Only in exceptional cases (such as happens in this video) we can appreciate its presence across the sky.

Créditos:

Video: Unidad de Comunicación y Cultura Científica (UC3), Instituto de Astrofísica de Canarias (IAC).
Timelapse: Daniel López.
Music: Neptune, by Nicholas Major.