I was at the airport last friday and there were some nice sun light rays, although not much of a good spot to take a picture. What weirds me out every time I see them is that they look as if coming from a ball of light pretty much right behind the clouds. I drew some lines to illustrate that:    I never stopped to think about this before. Why are they not parallel, is it some kind of illusion?  In case astronomy matters to explain this, the picture was taken at 7pm, February in central Europe.
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Consider this picture of sun beams streaming onto the valley through the clouds.    Given that the valley is only (at a guess) 3km wide, with simple trigonometry and the angles of the beams, this gives the result that the position of the light source is being a few tens of km away at most.   What is wrong with the analysis?
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Why is it that if I have two torches, each shining rays in perpendicular directions at perpendicular screens, such that the beams cross, then the images on the respective screens are independent of whether the alternate torch is switched on? In other words, why does light seem to pass through itself without interacting?  Apologies if this question is basic, and apologies if there is a similar question somewhere on the site but I haven't managed to find an answer.   Thanks,  A.
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I am wondering why some got a moon and others got a sun as Where in the World hat for the same action:   vs.   And is it possible two collect both e.g. from different sites? I only get moons…  I know that there has already been some spoilering .
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By analogy with the sun, whose light is apparently reaching us in 8 minutes, it means that we are only viewing the sun 8 minutes ago when we look up at it. However, what if we were eventually able to build powerful machines that could view light from say hundreds/thousands of years ago, wouldn't that mean we would be able to observe what anyone did at any given time (given that we know their rough whereabouts at that time, e.g. where they lived). I think this is more a question of: Do things we can observe die out immediately, or travel as light, or get stored somewhere?  (Sorry, I know next to nothing about Physics so please cut me some slack if I said anything naive/silly)
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Can anyone explain why I get these lines when taking photos in bad/weak lighting? Here are some photos.
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So, I am not sure I can reproduce it via images, but the steps are:  1) At night, open a window and have a look at the surface of the earth  2) Suppose there's an object that reflects a tiny amount of light  3) When you actually try to focus your eyes at this object, you either don't see anything (depends on the amount of light it reflects) or you can hardly see it  4) When you focus your eyes on something that is 3-10 metres away, you can easily see this object with your ambient vision. Not the details, but it seems that it reflects more light.   Why does it happen?
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Look at my scene:     Sun is rising and as you can see the scene is realistic; I mean, that what is in shadow is almost completely dark. This is correct, but i would like something less "dark", like an HDR.  These are some parameters i'm using:     This is my unique Light in scene (Sun):     I'm using also a Post-Processing profile with "Eye Adaption" unflagged.  Can you suggest me what i've to change to make my object affected by shadow less.. dark ?   Thanks
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The first-ever image of a black hole released this week was taken with radio telescopes, suggesting that it is a  image and doesn't represent what a person would see in reality, or visible light. This seems to be confirmed by this , but I am perplexed as to why this is not widely mentioned, including the announcement on the telescope's  and Wikipedia (, ). Perhaps not mentioning it makes for better headlines, but it feels wrong.  What's going on here?
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Why is an image formed when two light(one to the focus and one to the lens perpendicularly from the top of the object) rays coming from an object intercept?
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Background:  I've lived in Philippines for several years, and visited other parts of Asia occasionally (Singapore, Indonesia, Hongkong).  I just moved to Western Australia a few months ago and I realized that the sun is brighter here, in the sense that every after sunrise and every nearing sunset, the sun shines too bright that it is blinding. This happens almost everyday, so this isn't just some one off thing.  In Asia, this never occurred to me. The sun was always bearable to the eyes.  Why is this so?
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I'm trying to compute the shadow of 3D objects on the ground. To do this I'm assuming parallel rays from Sun origin.   Let's assume the Sun direction is given by azimuth $\varphi$ and elevation $\theta$ angles. So the direction unit vector is retrieved as:  $$ \hat{\mathbf{s}} = \mathbf{R}_y\left(\theta\right)\mathbf{R}_z\left(\varphi\right)\hat{\boldsymbol{\imath}}$$  where $\mathbf{R}_{x/y/z}$ are the rotation matrices along the $x, y, z$ axes given by, for example, Euler-Rodrigues equation, and $\hat{\boldsymbol{\imath}}$ is the unit vector along $x$-axis.  A point on a ray-line has the equation:  \begin{equation} \mathbf{r} = \mathbf{r}_p + \lambda\hat{\mathbf{s}}  \tag{1} \end{equation}  being $\mathbf{r}_p$ a point on that line.  A point on a general plane is given by the equation:  \begin{equation} \left(\mathbf{r} - \mathbf{r_0}\right)\cdot \hat{\mathbf{n}} = 0 \tag{2} \end{equation}  being $\mathbf{r}_0$ a point on the plane and $\hat{\mathbf{n}}$ the unit vector normal to that plane.   Ensuring the validity of both equations (1) and (2) allows to compute the $\lambda$ multiplier and retrieve the position vector of the projected point (writing $\tilde{\mathbf{r}} = \mathbf{r_p} - \mathbf{r_o}$)  \begin{gather} \lambda = - \left(\frac{\tilde{\mathbf{r}}\cdot \hat{\mathbf{n}}} {\hat{\mathbf{s}}\cdot\hat{\mathbf{n}}}\right) \\ \mathbf{r}_\text{proj} = \mathbf{r}_p - \left(\frac{\tilde{\mathbf{r}}\cdot \hat{\mathbf{n}}} {\hat{\mathbf{s}}\cdot\hat{\mathbf{n}}}\right)\hat{\mathbf{s}} \tag{3} \end{gather}  Applying eq. (3) to all the vertices of a mesh $\left\{\mathbf{r}_{p_i}\right\}$ .   A problem can be noted: $\hat{\mathbf{s}}\cdot \hat{\mathbf{n}}$ can be zero (e.g. Sun is horizontal, i.e. the ray is ortogonal to the normal of plane).   Are there some conceptual mistakes in my reasoning? Is there a way to rewrite the operation as a linear operator applied to the set of vertices position vectors?   $$ \left[\mathbf{A}\right]\left\{\mathbf{r}_{p_i}\right\} = \mathbf{r}_\text{proj}$$
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Simple question, I've always wanted to know the answer to this.  Why do you see a pair of lines radiating out from street lights when you squint at them? I can't think of a better way to describe what I mean, but I hope someone knows what I'm talking about.  Is it some sort of diffraction effect caused by your eyelashes acting as a grating?  Any ideas would be greatly appreciated :-)
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I was wondering how I can do this type of optical illusion. Is it done manually or is there a quicker way to do it. Thanks ahead of time.
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I've read a lot of answers to the questions why the sky is blue. However all the answers I found contain mostly qualitative analysis: Rayleigh scattering is changing the direction of blue light, so there is more blue light coming to the eye along the line of sight than the red one. However these explanations raise additional questions. First of all, the scheme of only single scattering seems to be an oversimplification: the light direction should be changed more than once. Can we prove that this is negligible by calculation, or is it not negligible? Does this change the analysis? Further, the explanation says nothing about the exact amount of the blue light being scattered when looking into a particular direction. Assuming the sun is in zenith, it follows from symmetry that the color of the sky in the directions having the same zenith angle must be the same, but closer to the horizon the way of the scattered light differs a lot from the rays coming near zenith — so is it possible to derive theoretically a formula which would predict the color of sky given the azimuth angle and the position of the Sun (at least in a simple geometrical setup when the Sun is in zenith)? It's not clear why the color should not rapidly change from near blue at horizon to almost red near the Sun position: after all, the atmosphere is thicker along the lines going closer to horizon! The sky seems to be more uniformly blue than the typical explanation suggests. Further, it follows from the usual explanation that blue light is partially reflected back into the space. Due to this, about half of all scattered light should be lost, so the total amount of red light coming from sun should be greater than the amount of blue light, which seems to contradict the observable reality. Does it? I'm mainly interested in quantitative analysis, not the observations or qualitative considerations.  I've read the answers to  and know that the physiology of the eye comes additionally into play, but let's neglect this for the sake of simplicity.
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I came across some really cool  today. How did he manage to get these photos? I couldn't find any EXIF information anywhere, and I don't have enough experience with macro to figure out how he did it.  It's obvious that the light has a lot to do with the result. How and what kind have been used? And what kind of camera equipment?
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I was wondering, is there any inherent difference between a still of a sunset and one of a sunrise, if you have no further context?  That is, without knowing the time when the picture was taken, where in the world it was, which way the photographer was facing etc. Just from elements in the picture itself. Is it possible to tell the difference?  For instance, if the earth rotated a lot faster, I assume you would be able to tell by the light trail (or, of course, if it was a long exposure photograph).  Ideas?
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I live at roughly $(52.4^\circ,-2.1^\circ)$. On sunny evenings I've often looked at the Moon and the Sun and noticed that the light part of the Moon does not appear to line up with the Sun. For example, at about 17:00 GMT on 13 Mar 2011, I noticed the half Moon was facing toward a point roughly $10^\circ-20^\circ$ above where the Sun appeared to be. Why?