HDR Lunar Corona by Boris Dmitriev & Stanislav Korotkiy at the Special Astrophysical Observatory of the Russian Academy of Science, Karachay-Cherkess Republic, Russia.  Images ©Boris Dmitriev & Stanislav Korotkiy, shown with permission.

A corona is a diffraction pattern in the sky produced by light interacting with small water droplets in clouds. It has a huge range of brightness. Most scattered light goes into the bright central aureole but even that is dim compared with the moon itself. The first ring outside the aureole has only 1.75% of the forward-scattered light intensity. The second ring is 4X fainter still at 0.42% and so on.

Our eyes cannot cope with the intensity range and we usually see no more than 2-3 rings. Cameras are worse and cannot capture the rings without grossly over-exposing the moon and central portions. Sometimes a fortuitous cloud does allow the lunar details to be preserved while capturing the outer coronal delicacy.

In the clear air of the 2,070m high observatory, four rings were seen visually and even more are on the image.  High Dynamic Range (HDR) techniques were used to render the brightness range. Individual images were made with a 50mm lens on a Canon EOS 20D using exposures of 1/1000, , 1, 2.5, 5 and 10s. They were combined in PhotoShop CS (File > Automate > Merge to HDR) followed by levels and curves adjustment.

The small images are from the original 1/1000, 1/2 and 10s exposures.





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