The incredible night photos and time-lapse movies NASA has been sharing with us provoke questions about our planet. That thin-yellow atmospheric line separating earth from space, for example, that we see in all of the night shots provokes two questions: (1) how thick is this line? and (2) why is this line colored the way it is?
The visible yellow and green/blue capped line represents atmosphere reaching ~100km above the surface of the earth. The colors are not reflected light, and not pollution, but rather are light generated from the components in the atmosphere itself. Yes, the atmosphere gives off its own light, in a chemiluminescent process called "airglow" or "night glow."
I have written a blog to accompany this video that explains the various colors of "Night Glow" and discusses the Aurora as well. I hope you find this blog a useful companion to understanding what you are seeing.
In particular, NASA astronaut Don Pettit has filmed and provided the majority of the available time-lapses. He is one of the explorers that truly understands how important it is for explorers to share the wonder of their experiences through both art and science. May all future explorers follow his lead.
These images were imported into Adobe Lightroom, cropped, rotated, and slightly tweaked. I had two main goals with the edits done in the manner I did them. My first goal was to bring the viewer's attention to the atmospheric line by focusing the cropping to prominently feature the atmospheric line and the "Airglow." Secondly, most of the images we see of earth show the planet at the bottom of the frame and space at the top of the frame. To remind the viewer that, in space, the orientation by which you chose to view planets is up to the viewer, I took artistic license with these images to present different ways to view our planet's movement in space.