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Under very dark skies the transparency of the atmosphere can change noticeably over a period of minutes ...

This is largely caused by excitation of oxygen in the upper atmosphere and can vary over scales of minutes, much as an aurora display but much more subtle.

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I don't think that airglow should be confused with transparency. Both of them can vary over short time scales, but they're two unrelated phenomena.

I've never seen a formal definition of transparency, and I doubt that such a thing exists. But it has to do with a reduction or transformation of the light from a celestial object. Extinction is certainly part of it, but maybe not all of it.

Airglow, by contrast, is perhaps best thought of as light pollution -- albeit natural rather than artificial. Same idea as an aurora, the zodiacal light, or scattered moonlight. It doesn't reduce the incoming light, but instead masks it by adding extra light both to the dark and the bright areas of the sky.

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Tony Flanders

First and foremost observing love: naked eye.
Second, binoculars.
Last but not least, telescopes.
And I sometimes dabble with cameras.

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