Mysterious phenomenon (and also embarrassing thing wot I did during a recent maritime aviation exercise):

Reported an aircraft inbound to the ship, facing us head-on (deduced from being able to see both its red and green sidelights).

It was inbound for a *really* long time.

It was, in fact, Capella.

I didn't even know it was possible for stars to twinkle red-and-green!

(Since then, I have been looking out for ones that do; the best examples I've seen so far being Sirius and Betelgeuse)

@ej The twinkling of stars is due to the changes in the density of the atmosphere, just like heat-shimmers over a hot road, on a large scale.

Like all transparent materials, the amount that air diffracts light is based on wavelength. All transparent materials split light like prisms all the time, it's just usually a very tiny effect.

In your case, essentially, the changes in atmospheric density were right to break colors enough for you to see.

Bad pre-coffee explanation, but hope it helps.

@icefox Thanks loads for the explanation - I really appreciate your taking the time and effort to provide one - but this does kinda seem to yield more questions than it answers!
• Prisms produce a static pattern (if you were in the "red sector" you'd see only red), but the star alternates between red & green?
• Only red & green, though the original starlight must have more than just those wavelengths?
• The atmosphere is constant for all stars, but only a few seem to do this?



I BELIEVE these are the answers:

* prisms produce a static pattern, but the atmosphere itself is moving around a bit, so you're looking through denser and less dense areas as you see the start. Imagine you're standing in one place and moving the prism back and forth a little as you look at it.
* I know the human eye is more sensitive to red and green than to blue, so with a faint light you might just see those colors most clearly?
* Again this might only happen with the brightest stars?

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@ej Those are my guesses from what optics and astronomy I know, at least. If you're a redditor then /r/askscience is a great place for this sort of question and you'll probably get far better answers.

@icefox Great answers! Thanks most awfully for taking the time to ponder!

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