Newton’s Rings

So here’s this double-pane patio door that, in colder weather forms this elliptical condensation patch

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near its center:

(For convenience, the following snaps are rotated 90° from those above.)

We surmise that when it’s cold enough the gas between the panes contracts so much that the two sheets of glass are pressed together to touch at one point, and the inside pane becomes a focus of condensation. Do you buy that? Close examination of the center of the condensation ellipse (wipe away the moisture first) reveals this pattern in the glass:

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a pattern always absent when the moisture is absent too. I think these are Newton’s Rings, a thin-film-interference phenomenon that he described. The contact point of the two pieces of glass is at the center of the rings, and the rings are richly colored by the mixing of different parts of the spectrum in different amounts. The same picture blown up and with the colors intensified but not changed in hue makes it clearer:

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In really cold weather the pattern lengthens, indicating contact of the panes along 4 or 5 cm of glass:

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suggesting an idea for a new thermometer.

Those colors are worth getting up in the morning just to inspect close up. And, when compared to the colors of a Soap Film (see elsewhere around here), it’s clear that both phenomena have the same underlying explanation. This first photo is snipped from the large one above, the second from a photo of a soap film:

But if similar spectra mean the same underlying explanation, what phenomenon produced this?:

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