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Airglow at Buenos Aires
Airglow is a very curious atmospheric phenomena. It is produced by emission of light in the high atmosphere by chemical processes. The result is a display of blueish or green bands that move quickly on the night sky. Airglow needs a very dark sky without light pollution to be photographed. To the naked eye it is usually colorless because the human eyes are not very sensitive to its color.
On December 12th 2012 there was a strong and unusual display of airglow near Buenos Aires, Argentina. I was in a rural location planning to shoot the Geminid meteor shower and was taken by surprise by this event. The bands could be seen weakly with the naked eye as if they were very thin clouds but in the photos a strong green color revealed its nature as airglow. This shouldn't be confused with the Aurora, from my location Auroras are never visible but airglow can be seen all over the world.
This video shows how the airglow patterns changed quickly at the North side of the sky. The pleiades are visible just on the left of Jupiter (very bright) with Orion on the right. The patterns danced for about 15-20 minutes and then suddenly disappeared. You will also see several planes and even some fireflies!
The display was even stronger to the South where the green bands contrasted strongly against the sky. The Magellan clouds can be seen here with the Large Magellan Cloud in the center of the frame. The Small Magellan Cloud is near the top of the frame with the globular cluster 47 Tucanae just next to it. It does look like the Aurora but it's not.
This stereographic projection shows the sky wrapped around a 360 degrees view of the location. The airglow bands can be seen clearly. These bands are paralell to each other but seem to converge because of perspective. The same that you can see with train tracks.
There are some reports about airglow increasing in the last months but it's not clear is this is because some natural cause or just because more and more people are shooting the night sky with better cameras. This case was particular because it was very strong, colored and near a very big city like Buenos Aires. I've photographed airglow before but only in very remote locations with very dark skies and no light pollution, it was my idea that photographing or seeing airglow in less than perfect conditions was impossible but I was wrong.
You can check the photos at this gallery.
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