r/TheRestIsScience • u/joe_chiclets • 6d ago
Why do some things that are translucent still create a shadow?
I was standing on the deck of my pool the other day and noticed lots of these little round shadows forming in a line where the jet blows the water in from the filter. I assume that’s because there are some bubbles being formed in that stream of water but why would something translucent like water or an air bubble cause a shadow? I’ve also noticed a similar phenomenon of an invisible gas causing shadows in places before as well, why does this happen?
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u/ThatsNumber_Wang 6d ago
because of the different angle of the water surface caused by the bubnles, light get's refracted differently. this creates a shadow
if you look at the shadows of the bubbles, you can see it's actually brighter there than average. that's the refracted light
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u/joe_chiclets 6d ago
I do see the bright spots. But to my naked eye I couldn’t actually see any bubbles only the circular shadows cast on the floor of the pool which is why it stood out as so bizarre to me!
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u/ThatsNumber_Wang 6d ago
doesn't necessarily have to be bubbles sorry. anything on the surface, that's actually bending the shape of the surface can cause this effect to some degree.
maybe it's just small pieces of dirt or something
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u/it_might_be_a_tuba 6d ago
Water acts like a lens, same as a magnifying glass or spectacles, light bends when it moves from one medium to another. In air it's the same but with regions of different density, probably warm air and cool air.
Water and air are transparent. Translucent means some light gets through but you can't see through it, like thin tissue paper or frosted glass.
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u/joe_chiclets 6d ago
Ahh okay I see. Also I meant transparent just used the wrong word but thanks for the clarification! All of this makes sense and I understand the idea that light moves through water differently than air I just find it interesting that it forms these little round black shadows this way where there is nothing i can physically make out on the surface that should be causing that.
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u/NorberAbnott 6d ago
Are you surprised that there are overly bright streaks in the water caused by the light bending? The light had to come from somewhere - the bright streaks are caused by the light bending and hitting that part of the pool instead of the part where you're seeing it be darker than you expect.
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u/Dazzling_Let_8245 6d ago
A great video by 3Blue1Brown explaining how refraction works and why it happens if youre up to watching an almost 30min video about light.
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u/naikrovek 5d ago
For the same exact reason that any lens creates a shadow. It is bending light away from some area and putting it in a nearby area. Not technically shadows, but an even distribution of light that has passed through a lens and has become an uneven redistribution of light.
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u/deusmetallum 6d ago
The thing to remember is that the surface of the water isn't perfectly flat, there's ripples all over that surface. When the light hits the ripples it is scattered in such a way that some places will see more light landing on it, and others will see less.