Diffused Sun/Moon Reflection: Why Water Appears as Columns

[Pranav Jha]

How would the reflected light from the sun or moon apear if the water surface were perfectly smooth?and why does reflected light from the sun or moon appear as a column in the body of water like here
http://www.free-slideshow.com/screens/waves_sunsets/sun-over-the-ocean.jpg

 

[K^2]

If it was smooth, it'd just be like looking at it through a mirror. Nothing interesting.

The reason why it appears as a "column' is far more interesting. The waves don't just diffuse the light, because they are not random "noise" on the surface. They are typically more or less moving in one direction. That means that besides random bumps, that are there, there is prevalent direction for the curvature. So given direction of the wave motion and direction from which the sun light is hitting them, there is an entire plane into which the sun light is reflected. That means that a point source, rather than being reflected as a point, will appear as a line in the reflection.

Another place you see this is glare on hair. Consider http://jasonchristopher.com/gallery/1210724957_silky-hair.jpg . Note that the glare on the hair is distributed along a patch that is stretched in direction perpendicular to the direction the hair is laid out in. Just like the sunlight reflection is stretched in direction perpendicular to the waves. It is exactly the same effect.

 

[Pranav Jha]

So given direction of the wave motion and direction from which the sun light is hitting them, there is an entire plane into which the sun light is reflected. That means that a point source, rather than being reflected as a point, will appear as a line in the reflection.

could you please explain this part more clearly?
by the way, i wasn't able to access the picture

 

[K^2]

Odd. Well, look at pretty much any picture with shiny hair in it. You should be able to see that the shiny patch tends to run in direction perpendicular to direction of the hairs.

Lets start simple. Imagine a shiny sphere. Somebody is shining a flashlight on it. No matter where you are standing, as long as you and the flashlight are on the same side of the sphere, some of the light from flashlight will be reflected your way, because there will be at least some spot on the sphere where the angle of the surface is just right for light to be reflected towards you. So if you built an entire wall made up of small spheres and shine light on it, pretty much the entire wall is going to appear to shine.

Now imagine a cylinder instead. There are now two angles. One is the angle between you/source and the cylinder's axis, and the other angle is the angle around the cylinder. The later is irrelevant by the same argument. No matter where you are, there will be some part of the cylinder where this angle is just right. But the angle with the axis is fixed, so that angle has to be just right. So if you take a whole bunch of cylindrical rods and build a wall out of these then shine some light on it, you'll see a patch of reflected line running across the wall perpendicular to cylinders.

Does this help?

 

[Pranav Jha]

Now imagine a cylinder instead. There are now two angles. One is the angle between you/source and the cylinder's axis, and the other angle is the angle around the cylinder. The later is irrelevant by the same argument. No matter where you are, there will be some part of the cylinder where this angle is just right. But the angle with the axis is fixed, so that angle has to be just right. So if you take a whole bunch of cylindrical rods and build a wall out of these then shine some light on it, you'll see a patch of reflected line running across the wall perpendicular to cylinders.

Does this help?

it helped a bit. I understood the part on sphere. I tried my best to understand the explanation furthered to a cylinder but i couldn't understand it. I don't understand what you mean by "TWO ANGLES" (probably a diagram would be helpful). After that, i couldn't get anything that followed.

 

[johng23]

Science can sometimes be hard to explain in words. When light hits a flat surface, it is reflected at exactly one angle. Now think about the situation for a sphere or a cylinder. It doesn't need more explaining, you just need to think about it.