# Reflection of the sunlight on water

#### NobleOne

##### Member
We all know that reflection of sunlight on water at sunrise/sunset is dependent on observation point. But I'm scratching my head with next question. If I'm looking this reflection at one point and another observer who is 1Km away at the shore is looking the same thing, why is it that I can not see what he is seeing if light reflects from water. Does photons carry brightness with them if light travels as physics says? If so shouldn't I see both reflections or shouldn't the whole sea be bright, having reflected sunlight everywhere?

Because the eye-water-sun angle needs to not vary much to see the reflection. Looking to the side makes the angle too much.

It's a fun problem. Try recreating it with aluminum foil.

There are two ways of reflection: specular reflection (like in a mirror) and diffuse reflection (like on a wall). The reflection you see in the photograph is mainly specular reflection. There the incident ray and the reflected ray have the same angle with the surface. Because the water is not perfectly flat, you don't see a perfect reflection of the sun. If the water IS still perfectly flat, you actually see an image of the sun like this

On the other hand you have diffuse reflection. If you shine the beam of a torch on a wall you can see a light area on the wall from all directions. because the rough surface of the wall reflects the light in all directions.
But the sun is not a torch with a concentrated beam, so you cannot see one spot or area (unless it is cloudy and only a small area of the surface is lighted by the sun).

You only see the photons that end up in your eye.

The photons forming the bright reflection that your friend sees end up in his eye, not yours.

You can still see some light on the sea in those areas, of course, but that is just photons that have been scattered sideways rather than the main, bright, direct reflection.

or shouldn't the whole sea be bright, having reflected sunlight everywhere?
You do have reflected sunlight from everywhere, because of the diffuse reflection. Of the infalling sunlight a portion is reflected specularly, another portion is absorbed, a third portion enters the water and finally a portion is reflected diffusely. And every patch of the surface only reflects diffusely a small percentage of that last portion in your direction (the rest goes in all other directions). The ratio of all these portions depends on the angle of incidence of the light ray.

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If so shouldn't I see both reflections or shouldn't the whole sea be bright, having reflected sunlight everywhere?

Imagine you are at point A and your friend is at point B.

Most light bounces in a fairly straight line from the sun, off the water, to each of your eyes. So you will see the reflection at the point where the red line hits the water, and your friend will see the reflection where the green line hits the water.

But there is also a smaller amount of light scattered in all directions by the rough surface of the water (the small arrows). That happens pretty uniformly all over the sea, so what you will see then you look to the point where your friend sees the bright reflection is just the background random scattered light. Same when he looks towards the reflection you see.

(Imagine that there are lots of those little arrows randomly in all directions all over the water)

Try also experimenting with a dark container with water. A large tray would work. Use a small light for the sun. Experiment with angles and still vs rippled. Compare to foil, smooth or wrinkled.

Something like this:

You see a line because with small ripples it's only along that direct line, and with a very low camera angle, that a small change in angle will result in the sun reflecting in the camera. If you move away from this line then you need additional slope to reflect back towards the light. So for the directly reflected light to spread out the ripples need to be larger.

Dr. Joseph Shaw is the go-to expert on glitter patterns.

https://www.esrl.noaa.gov/psd/outreach/education/science/glitter/

External Quote:
The name "glitter pattern" implies a moving and changing phenomenon. Glitter patterns consist of many bright points of light that come and go, blending together to form a smooth path of glittering light when viewed at a distance. If you look closely at a glitter pattern, you can see individual points of light. Each of these points of light is a specular reflection of the sun, called a sun glint. Glints occur on the water where the local slope provides a direct specular reflection of the sun. A perfectly smooth surface would contain only one glint.
The trail is actually made up of numerous individual images of the sun. If you looked at each one, you would see a more or less recognizable image of the sun. But they are distant, there are a lot of them, and they come and go in an instant.

Think of each little wave as a little mirror and seeing the sun in a thousand different little mirrors. Each one is at just the right angle to reflect to your eye. So in a sense the trail you see is unique to you. That other guy is seeing his own unique trail too. But they are very similar.

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I remember having this thought before, except it was about seeing the reflection of the sun on a car. Why wouldn't the entire car be awash with blinding light? Thinking about it, though, I realized what Trailblazer described above: only a certain area of the car would reflect the photons from the sun directly into my eye, and that area was the spot where I was the image of the sun.

Instead of thinking about how the sunlight is cast in all directions, think about your own cone of vision. You can picture it as a series of "rays" that converge on your eye(s). Only photons that travel in a path along these rays will be in your vision. So as the rays of light fan outward form the sun, only some will line up with the "rays" that converge on your eyes. It's in those areas that you will see an image, in this case the reflection.

This explanation sort of assumes that we're talking about theoretical points of light rather than real objects with size and mass, but if you imagine that every visible point on the sun is radiating photons in all directions then there will be one ray of light that travels from that point to your eye; do this for every point on the sun and your eye sees an object. The reflection is causing the other rays from those points to bounce in different directions, and some of them are directed into your eye. Others just bounce off elsewhere and scatter, meaning they don't make the same bright reflection as the direct ones.

Be sure you understand the idea of "specular reflection." The difference between matte black and gloss black is something that puzzles people... to the point that I've heard it in a stand-up comedian's routine.

Both from Wikipedia:

External Quote:
Reflection of light is either specular (mirror-like) or diffuse (retaining the energy, but losing the image)
External Quote:
Specular reflection is the mirror-like reflection of waves, such as light, from a surface. In this process, each incident ray is reflected, with the reflected ray having the same angle to the surface normal as the incident ray.
Matte black is simply a surface that minimizes specular reflection; what we see is mostly "diffuse reflection." Gloss black has a hard smooth surface. So you get specular reflections off that hard smooth surface.

It's so much more complicated than simply rough and smooth surfaces that I have to refer to the wiki article:

https://en.wikipedia.org/wiki/Diffuse_reflection

External Quote:
When light strikes the surface of a (non-metallic) material it bounces off in all directions due to multiple reflections by the microscopic irregularities inside the material (e.g. the grain boundaries of a polycrystalline material, or the cell or fiber boundaries of an organic material) and by its surface, if it is rough. Thus, an 'image' is not formed.

No matter how smooth and polished the surface of a material like this is, it won't be a mirror. But when you have a really smooth surface, you get an increase in the amount of specular reflection.

In clear water you can see past the surface but you also get specular reflections. I suspect that the reason you get specular reflections off of water is that the molecules at the surface are cohesive and create the condition called surface tension. Glitter trails are specular reflections off of the smooth (though irregular) surface of water.

A car is an object with an irregular shape. But this is the way a gloss surface on a regular shape reflects light.

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Something we haven't mentioned that might be a part of the OP's puzzlement is parallax.

External Quote:
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.
Because the sun is very distant, both you and your friend a kilometer away will see the sun in the same compass direction. So don't imagine your distant friend having to turn his head to see "your" glitter trail. He will be seeing his own unique glitter trail. If you are looking due west, he will be looking due west too. Exactly.

I can't find a video like this with a sunset over water so this will have to do. The reason the sun "paces" the car is because it's so distant. You don't have to turn your head to keep the sun in view. But you have to turn your head to see the trees and buildings, because they are closer.

If you imagine this was on the shore of a lake, you'd see a glitter trail "pacing" the car too. In a sense there is a glitter trail across the whole lake, but you have to be in just the right spot to see each part. You can't see the whole thing at once. You can't see the specular reflection of the sun on the whole lake all at once, only a part of it at a time. So you are seeing one part and your friend is seeing another part. His glitter trail won't be visible to you and yours won't be visible to him.

But you can see the diffuse reflection of the sun (and sky), what we call sunlight, or a sunlit lake, across the whole lake all at once.

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Try also experimenting with a dark container with water. A large tray would work. Use a small light for the sun. Experiment with angles and still vs rippled. Compare to foil, smooth or wrinkled.
What about adding a heating coil (hot plate) just under what you would consider...."the horizon" (or near horizon)
Could you make a miniature "mirage" ? I never tried it.

What about adding a heating coil (hot plate) just under what you would consider...."the horizon" (or near horizon)
Could you make a miniature "mirage" ? I never tried it.

Not a stable one. You could get some shimmering though. The warm air would be continually rising.

You only see the photons that end up in your eye.

The photons forming the bright reflection that your friend sees end up in his eye, not yours.

You can still see some light on the sea in those areas, of course, but that is just photons that have been scattered sideways rather than the main, bright, direct reflection.

Thanks! This is the answer I was looking for. I wrongly thought that photons carry brightness with them but the reality is that only thing that photon is carrying is the information for our eye which then interpret it as brightness when is stimulated by the wave of photon. I'm referring here only to visible light. All other EMR excluded (heat, etc.)

According to this, we actually do not see the whole picture with our eyes. Since there is EMR everywhere, only a small fraction of it reaches the eye and if we could see (interpret with sight) every single photon all we would see is brightness or light. Correct me if I'm wrong here.

Also, hypothetically speaking, if someone could control the Sun, at least those visible EMR, some very deceiving effects could occur for targeted person. What is even more scary is, if done right, any person standing next to targeted one would not see what targeted person sees.

I'm wondering if there is some technology out there which can modify those visible EMR, not from the Sun, but between the Sun and observer.

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I also want to say: thank you all for your generous responds. I've also done some experiments in my mind and then checked if light really bounce from the surface at the angle which came onto it.

A darkened room with pocket laser and some smoke showed it does.

Glitter trail on a wave. FE Believers cite glitter trails on the ocean as proof that the surface of the ocean is not curved. They insist (it's only common sense!) there can be no trail on a curved surface.

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