Seeing a night sky free of light pollution is one of the most awe inspiring views. On a dark moonless night hundreds of miles from civilisation, the Milky Way shines clearly in the sky and thousands of stars can be seen with the naked eye — but the sky isn't black, at least not usually.

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To those who have never seen a truly dark sky site before, this may come as a surprise. You might expect everything to be inky black, but instead it takes on a faint gray glow, seemingly brightening as your eyes adjust to the dark. Some nights that gray glow seems to become almost bright enough to mistake for light pollution, particularly around the horizon. In a sense, this is light pollution but it isn't artificial, it's a natural light emission known as airglow.

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​The presence of airglow in the sky ensures the night is never truly black, and with the use of cameras, airglow reveals itself to be full of brilliant colors, greens and reds are most common.

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