Colour in the air

Located deep in the Chilean Atacama Desert, far from the light pollution associated with human activity, is ESO’s Paranal Observatory: a world-leading research site that enjoys some of the darkest skies on Earth. Paradoxically, it is this extreme darkness that allows the sky to light up in technicolour in this image. 

The striking radiant light visible in the sky here is a phenomenon called airglow, which lends a magical appearance to the already breathtaking night sky. As the name suggests, airglow is a faint glow in the air created as atoms and molecules in the atmosphere combine and emit radiation. It is only visible in regions where the sky is dark enough that artificial lights do not overwhelm it. This phenomenon was the subject of ESOcast 78.

This perspective was captured from the site of VISTA, the Visible and Infrared Survey Telescope for Astronomy. The trail of faint yellow lights along the ground leads towards Cerro Paranal, the mountain in the centre of the image, where ESO’s Very Large Telescope (VLT) is just about discernible at the top. The bright band of stars that forms our home galaxy, the Milky Way, appears to arc over the mountain, infused with the colours of the atmosphere.