Timeline for Why do shadows from the sun join each other when near enough?
Current License: CC BY-SA 3.0
10 events
| when toggle format | what | by | license | comment | |
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| Aug 26, 2019 at 10:09 | comment | added | Azzinoth | You can observe this yourself. Put your hands together such that only your thumbs are free and move them very close before your eye. Then look through the small slit between your thumbs and focus a bright surface behind that (for example your computer screen). Try to vary the slit width and distance with your thumbs. Eventually you will see, that a pattern of multiple dark lines and white lines appears between your fingers. If you move the thumbs closer the dark lines become broader until they merge into the black drop effect. Diffraction has to be at least part of the explanation. | |
| Jun 8, 2019 at 12:41 | comment | added | Sam | Might not be evident, but it's still correct. The accepted answer mistakes digital camera artefacts for optics effects. | |
| Jun 8, 2019 at 9:07 | comment | added | jinawee | @Sam This answer provides no calculations or experiment, so it's not evident that it's the correct answer. | |
| Jan 29, 2014 at 12:48 | comment | added | gigacyan | @JohnRennie diffraction affects all light, whether coherent or not. When it is coherent, you see nice fringes, and when it is not - just blurring, like in this example. | |
| Jan 21, 2014 at 9:06 | comment | added | Sam | An easy way to have a perfect point source is a cardboard with a very small hole in it. Put it in the window in a sunny day. | |
| Jan 20, 2014 at 19:27 | comment | added | turnip | @JohnRennie This has me thinking a lot now. Some people say it is diffraction, some say it is penumbrae. Hmm. If it was diffraction wouldn't there be a diffraction pattern formed of light, not one formed from a shadow? The bulge seen in my video does look a lot like a diffraction pattern which may be confusing people. | |
| Jan 20, 2014 at 17:42 | comment | added | John Rennie | I can see the same effect with shadows on my living room wall lit by the long life bulb in the room. Since this not an even approximately coherent light source I'm disinclined to believe it's diffraction. However there is an easy test. If it's diffraction it will still be visible with a point source of light, but if it's overlap of penumbrae it will disappear if a point source is used. The two theories predict exactly opposite behaviour - if only all experimental physics was as clear cut! If I can find something to act as a point source I will attempt the experiment. | |
| Jan 20, 2014 at 13:27 | comment | added | Sam | This is the only physically correct answer - I do not understand why completely unrelated answers get so many upvotes. | |
| Jan 19, 2014 at 12:56 | review | First posts | |||
| Jan 19, 2014 at 13:08 | |||||
| Jan 19, 2014 at 12:39 | history | answered | user1008646 | CC BY-SA 3.0 |