# Why do sun rays fan out?

Really, I am. It seemed an interesting question and I am always glad to smoosh my own ignorance to whatever degree.

So, having already starred in this thread as the guy who had a thought but didn’t really know the answer, but ran with it anyway, (and got thoroughly SDMB’d) let me pursue said thought. When I read the OP, I didn’t pick up on sunsets, raypaths of light travelling across the curved sky above, etc. I pictured only the case of an overcast day where a hole appears in the cloudcover and a shaft of sunlight penetrates. When viewed, said shaft of light can appear to widen (fan, I guess). While obviously not the primary answer to the question of why, I must ask: does not diffraction occur and, at least, contribute to the perception? If not, why not? An existing but negligible contribution, perhaps?

And as to why I used “if your more ambitious” instead of “if you’re more ambitious”…well, I was just having a great day.

The sun’s rays fan out because otherwise Birdman would hog them all.

beatle, I’d say you’re right in that diffraction is “an existing but negligible condition”. Perspective is the greatest factor by far. Consider this picture. The point that the rays converge is obviously where the sun is. The angle between the (for all intents and purposes) parallel rays is due to the fact that they are coming almost directly at you, so the perspective is exaggerated (see also: railroad tracks). Imagine a ray going from the sun to your left cheek, and then imagine a ray going from the sun to your right cheek. These are parallel, but due to your point of view, will appear to intersect at a sharp angle.

Diffraction will tend to make the edges of the light “beams” fuzz out very slightly, but the fact that the sun is a very large light source (as opposed to a point light source) has the same effect to a much larger degree, so I think the diffraction is probably imperceptible.

Aside: I love the comment below that picture: “This image is protected by a digital watermark.” What digital watermark? It must be very subtle. :rolleyes:

It’s not so much a joke as it is a mealy mouthful of weird words sure to impress people at cocktail parties, assuming people still have cocktail parties.