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I've noticed that in this outdoor swimming pool, the near and far sides of the black racing stripe appear blue and orange, respectively.

photo

I've drawn some ray diagrams trying to rationalize this, but I can't get a satisfactory answer for why the light that experiences a higher index of refraction (blue) should appear on the near side of the black stripe, and likewise for red. Shouldn't the bottom of the pool emit light equally in every direction? If so, how can different sections appear as different colors? Sorry if the phenomenon isn't clear in the photo; if it isn't, just take my word for it.

My best guess is that, for whatever reason, light is preferentially emitted upward. So, that light is separated with blue hitting the bottom of my cornea and red the top. This feels wrong to me. Anyone have a better explanation for this dispersion?

valen
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2 Answers2

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Why? That phenomenon is perfectly reasonable.

Recall the fact that refractive index of water is greater for violet than for red. Consider this fact, let's construct ray diagrams.

Recall Snell's Law:

$$\mu = \frac{\sin{i}}{\sin{r}}$$

Here, we consider the ray from inside to outside water, so we get $\mu = \frac{3}{4}$. Red would give a value of $\mu$ slightly more than $\frac{3} {4}$, while violet would give a value slightly less than $\frac{3}{4}$. This is because for a given colour of light, $$\mu=\frac{c}{v},$$ and we know that red light travels the fastest, hence the fraction $\frac{c}{v_r} < \frac{c}{v_v}$. This directly implies that red light gets refracted the least and violet the most. As a result, the value of $r$ is more for violet than for red.

Red will appear to bend less than the mean deviation and violet will bend more. Trace their backward paths, you get:

enter image description here

I hope this helps.

Community
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Pritt Balagopal
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I'm no expert and I am not claiming that this is the actual answer but I think it is a possibility. I think it is a result of chromatic aberration. I won't go into mathematical detail but show you some pictures of the results:

enter image description here

(Image by George Shuklin from wikimedia released under CC BY-SA 1.0)

This webpage also gives a picture which shows the blue and orange edge due to chromatic aberration. I won't reproduce it here since I don't know the licensing on it.

You talk about the cornea in your post - indicating you see it with your eyes as well as with a camera. This post by BarsMonster explains how we do have chromatic aberration in the eyes, but our brains usually account for it. I suspect (although could be wrong) that in this case the aberration is exaggerated.

Quantum spaghettification
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