Chilean sky images by Yuri Beletsky. All images ©Yuri Beletsky, shown with permission
Top:Banded red oxygen and perhaps OH airglow dominates the sky over Paranal's 4m VISTA Visible and IR Survey Telescope. Some green oxygen is also there.
Left: Red banded airglow silhouettes the Cerro Paranal VLT platform. The Large and Small Magellanic Clouds shine through the glow.
The bands resemble crepuscular rays in appearing to converge to a point to the left of the Paranal telescopes. Their movement through the night is in this time-lapse video.
The bands are are actually huge parallel structures in the thermosphere 90 km upwards. Perspective makes them appear to converge.
Gravity waves propagating upwards from disturbances lower down in the atmosphere are likely the source of the bands. The wave amplitude increases with height (reducing density) and wavelengths can be thousands of kilometres.
Lower: Airglow at the horizon at Carnegie Las Campanas Observatory. In the foreground are the two 6.5m Magellan telescopes.
|More bands across the Paranal VLT sky.
While telescope placement can optimise seeing and avoid (to a decreasing extent) human light pollution, airglow is all pervasive.
|The dominant airglow emissions are usually green atomic oxygen (90-100km) and red oxygen at 150-300km. Hydroxyl radical emissions from a thin layer 86km high are weaker and rarer.|