Explaination for an Optical Phenomena

I would have to get my textbook out and go over the phenomenon, it is complex (for me) and involves some math.

I thought you wanted a basic explanation so I provided one.

A better explanation is that it works like a lense. If you were to find the focal point you would see that it is actually an image of what is on the other side of the hole. One of my professors explained that in some ancient time this was observed because of light going through a crack in wall projected an upside down image of people walking by outside on the opposite wall.

It has to do with the fact that light reflects off an object in a straight ray and in going through the tiny hole the light from the top of an object passes in a straight line through the hole and projects an image on the opposite wall, light from the middle goes straight through and light from the bottom goes to the top of the projected image. Here is wikipedia's explanation on it.

Drew K

He gave you an explanation, you didn't half understand it.

If you look at the projection very close to the hole, it will have the shape of the hole, as you move away it will assume the shape of the appearance of the sun. Usually round, unless during an eclipse.

If the hole is small and distance is enough, you can see the sunspots on the surface of the sun in the projection.

There's nothing mysterious or quantum about it. It doesn't even require the wave nature of light. Geometric optics and ray tracing explain it all.

If you are talking about a small hole then the camera obscura effect is ALSO in play. The simple fact is that the light patch IS the same shape as the hole. If you make a long slit ( say a small gap between two large sheets of ply ) and look at the light patch you will see that is indeed nothing like a round spot. Look again and you will see that the edges are not distinct. Why is this? Try again with thicker ply, or even two boxes, what happens now? Now try with sheet metal.

Place the sheets vertically and look at the light patch at the bottom and then at the top, what is the difference? ( I am assuming that you are in about the 30 deg latitude ) If the sun is directly overhead you would need to tilt the array to get the effect.

While you are playing in the sun take two planks of wood and place one 40cm or so off the ground to make a sharp shadow and the other at about right angles to first bit and raised two or three meters off the ground. Now look at the intersection of the two shadows and pay particular attention to the fuzzy bit on the side. What happens here?

Have fun, and who knows you may even be able to answer your own question.

Jim

Search 'pinhole camera'

interesting observation in my opinion..Explainations given are weak at best..this out of the box observation .has never crossed my mind in these 6 plus decades of life under our sun...Thanks..for pointing out something i had never thought of before..Light being just a small part of the total electromagnetic spectrum is amazing but again most of our reality is limited to that thin band of wavelengths and frequencies amplified i guess by the inheret photon effect to the point where our optic nerves can pick it up and our brains interpret the electrochemically transmited image...its all amazing and simple explainations while good forget the total magic involved...seriously

"Explanations given are weak at best"

That, or understandings -

OK, I'll take a shot. If you have a very small hole, the image of the sun will be a larger circle, because the sun is not a point source but is a circle with a diameter of about half a degree. Now consider that a larger, odd shaped aperture is composed of a lot of small holes merged together, then the image is a lot of larger circles merged together, which looks a lot like a larger circle.

Very near the hole, indeed you get the projection of the hole, and sunlight is traveling so far, 93,000,000+ miles, therefore the light is well collimated (parallel rays). But farther from the hole, it is merely an aperture and due to the slight angular spread from the left to right of the sun's projection, you receive a mini-image of the sun, as in a pinhole camera that takes a picture without a lens.

In answering the question it is necessary to consider that the hole is made up of a large number of small holes which each act as a pinhole camera producing a large number of sun images on the screen. Each image is rounded and each one overlaps the next image. The resulting image is equivalent to that produced by an out of focus lens. The blurred image is what we all see when our eyes become unable to focus as we age or have short or long sight. I once saw a picture of such images produced as others have said by a solar eclipse shining through the leaves on a tree. Also the suns rays are not parallel and the angular seperation between the light from the top and bottom of the sun give the resulting upside down image seen as they pass and cross at the holes.

I beg to differ. The sun's rays are certainly more well collimated than most light that is produced in an optical system other than a laser.

James the angle is small at around 0.5 degrees but without this angle we would not see the umbra and penumbra during an eclipse. I agree that for most purposes its parallel. Lets not fight over it.

0.5% seems overkill.

I know you proposed to not fight, but I can't find any other heated discussions going on right now on CR4.

Would it be possible for you to reconsider and the two of you to proceed with a knock-down drag-out fight about collimation?

You want fight? Here you go!

He said 0.5 degree!

your 0.5% is way of when talking about 180 degree of what I deem is parallel.

Come out and fight!

PS Am I too late????

Indeed, I erred. Good catch.

I'll own my mistake, even though I'm going to put a little blame on the silly fact that my keyboard doesn't seem to have a degree symbol ^{(other than the top part of the percent symbol)} Do you happen to know how to create the little degree circle?

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Back to the challenge at hand....

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When you wrote '...your 0.5% is way of when....' you use of 'of' (a preposition) was probably way off (part of an adverbial phrase when used as way-off).

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BTW, You aren't too late.

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So how far off does something need to be before you consider it 'way of'?

If we take your suggested reference at 180 degrees, 0.5% of that would be 0.9 degrees. Does 0.4 degrees count as 'way of'?

In CR4, click on the Ω ohm symbol next to the smiley face and find it there° it is the tiny circle toward the top left of center.

In ms word 03, I have to click on insert tab then symbol and get a pop up screen with lots of images to scroll through. In ms word 10 (and 07?) you click on a tab on the top right that has a symobl Ω again (I think) and you get a pull down with lots of symbols to choose from.

Or if you are keyboard savvy you can set up a keystroke shortcut to do it. From the programed ones I use cntrl - for subscript and cntrl shift + for superscript (or was it = for subscript?)

Drew K

Much thanks!

Gosh, where is me English when I need it!

Do you give up?

Way off is when it is less than what you say minus 1.

Anyway if you aim for the moon you should be fine with 0.4 but if you aim for the sun you will be way off!

'...Way off is when it is less than what you say minus 1...'

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Hmm. Interesting.

So, as long as I never overestimate, then I can avoid being way off.

That could be really useful. For example, if I know the answer is constrained to the set of real positive numbers, without knowing the question, I can answer '1' and know with certainty that even though it might not be the actual answer it is definitely not way off.

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Q: How many humans were on earth at 6AM GMT 01/01/2013

A: One

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Not exactly right, but not way off.

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I also like the fact that qualification of 'way off' can be manipulated by the choice of units. Avoiding 'way off' in terms of arcseconds is a much more stringent than avoiding 'way off' in complete revolutions.

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I think there are several good arguments that demonstrate by your definition that while I might not have been exactly right, by many measures, I wasn't 'way off'.

Your answer would be even more accurate if you stated the population was ≥ 1!

Drew K

I count myself as a human → population ≥ 1. If there are no other humans, I don't have to justify that to anyone....

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If there are other humans then I still don't have to justify it b/c they satisfy population ≥ 1.

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My original was accurate. Not only that, it was concise.

Yes, but can you prove that you exist outside of your own consciousness? Is the cat alive? If a tree falls does it make sound? Did Pavlov's dogs salivate because of the pending treat or because they knew if they salivated they would get treats?

mmmmmhmmm....treats..._{I'm off for coffee and donuts!}

Drew K

Ok fight on. The 0.5 ° refers to the angle where a line coming from the top of the sun meets a line coming from the bottom of the sun crossing at the pinhole. Parallel lines are at 0° by comparison not 180°. So the difference is not huge but big enough to affect the outcome. The sun is 1,000,000 miles in diameter (approx) and 93 million miles away (approx). Using the small angle approximation r=dsinø where d is the diameter and r the distance away we get around 0.5º for the angle. If the rays were at 0º we would get no image since the sun would be a point source producing just a dot on a screen.

Your turn

Ouch.

Um, well...

Oh yeah! I was referring to radians not degrees ^{(that is obviously the explanation, since it is the only where I might come close to approximating the appearance of having been 'right')}.

All civilized people use radians. I mean 'degrees' are in, what; base 60, mostly but not entirely. right?

How positively savage. I was just going on the assumption that you are also a civilized person. Yes, of course you are. Silly of me to even consider otherwise really.

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Okay. So now that we are all on the agreed upon correct civilized figurative page...

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We are typically at least 1.46 x 10¹¹ meters away from the sun.

The photosphere of the sun is typically no bigger than 1.40 x 10⁹ meters in diameter.

So the angle will be:\

tan^-1 (1.40/146)

= 9.59 x 10^-3 radians

which is pretty darn close to 1% ...of a radian (of course).

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I would like to preemptively explain that the whole uncivilized use of 'degree' units is likely the reason that my initial assertion that '0.5% seemed to be overkill' cannot be easily reconciled with the preceding explanation in this comment of mine.

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I miss Smokie. I'm trying, but know my attempt at disparate disjointed argument kung fu, doesn't even come close to master Smokie. I guess you can't be your own non sequitur strawman.

No further argument from me. Everything is relative.

Dear gurus and friends- I thought to begin this post with a confesssion that after I spent much time today with observations about the round sun light spots that I'm now cofused, but all of a sudden I went out again to the sun with a big wooden board that a 35*200 m.m slot is in it, and I had a square piece of steel sheet with me, I raised the board, so that the sun rays [in 2 hours sunset] will hit it and pass the slot in front of me was the western wall of my appartment.So the sun hit now this wall.

As the slot was open, the sun rays drew a precise light image of the slot on the wall, as I placed the steel square in the slot, so that it covered partialy the slot, but not parallel! I hold it diagonal, so it was like a triangle that divided the slot, but the bottom of the triangle was closer to the slot's end.

When I hold the board far enough, instead that the image of the upper side of the slot, close to the triangel would be triangle shaped- it became rounded!

This morning, I tried to find out about this phenomena, and I saw that I have 2 small hole in the asbestos roof the hole of my veranda, that the sun rays created a round image on the floor. If I covered partialy the hole with some solid object smaller than that hole the image on the floor continued to be round but partialy shaded!

Then I took a straight jaws plier and hold it so that it's shadow will fall on the wall, as it was full open, there was nothing sepecial, but as I close it little bit, the image on the wall became as if the plier's jaws were close to each other at the end, but they were not!

I found a name for this :Induced shadow!

My guess is that all this phenomena is resulting not of optics rather than interaction, rising up with the surounding, atmosphere!

Am I right?

Good to see that you are prepared to experiment. Try the two planks intersecting as i said in post#6. You will see an interesting induced shadow at the intersection. I am sure you know that light comes in 'packets' called photons that behave as waves. What is not immediately evident from this description is that the 'wave' is propagated in all directions. Think of a snake or worm swallowing a meal. The wave hits the edge of the solid and sprays about like water through a nozzle providing some light to the area that should be dark.

Look at this page; en.wikipedia.org/wiki/Double-slit_experiment for some more fun.

JIM