Author: Beth Ruggiero-York
Have you ever noticed a green or sometimes purplish glow in the sky of your night images? I’m not talking about the Northern Lights. It’s a bit less distinct than that. What I’m talking about is “airglow,” a natural phenomenon caused by various processes and chemical reactions in our upper atmosphere and prevents the night skies from being completely dark, even with all other light pollution (including stars) removed! Airglow is an aurora-like phenomenon, but it is rare to see with the naked eye. Longer night exposures, though, will reveal it in your photos. Without explaining the science behind airglow, what you need to know is how it affects your night images, and whether to embrace it or try to eliminate it.
My first encounter with airglow was the same night as my first encounter with aurora. I don’t think it was a coincidence at all, but in both cases that night at Mono Lake, I had no idea what I was seeing. After photographing the night sky over Mono Lake and seeing a bright red glow showing up in the images, which I dismissed as light pollution from Reno, I turned south to photography the Milky Way rising. As odd as the red glow over the lake was, even odder was the green glow of the Milky Way – a strong green glow. Here is one of the original, unprocessed images from that night.
At the time, I thought something was wrong with my new Sigma 35mm f/1.4 Art lens or my camera body, the Nikon D800e. I “color corrected” the images, and everything looked normal, but I kept the original greenish images.
That I was able to correct the color and eliminate most of the green cast (it is still visible close to the horizon) shows that it can be corrected out of your images.
Several years later, though, I am not so sure about eliminating this natural phenomenon from my night images. In fact, the more I learn about it, I have decided to embrace it. After all, would you try to get rid of the colors in the night sky that we know as Northern Lights?
[Check out this amazing image of airglow in Chile less than a month ago: http://spaceweathergallery.com/indiv_upload.php?upload_id=117043]
For answers to all your questions about night photography, check out my book, Fun in the Dark: A Guide to Successful Night Photography, at www.funinthedark.net
Blog post by Beth Ruggiero-York, photography instructor for AHPW