Timeline for How do you aim a signal mirror?
Current License: CC BY-SA 3.0
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| Apr 28, 2017 at 23:38 | comment | added | sdenham | @JamieHanrahan But that means you have to get the mirror to within a 1/4 degree angle window in two dimensions (because reflected beam's angle change is twice that of the mirror). If you are trying to attract attention, wiggling it around approximately the right direction should suffice, but to send a message, you probably need some aiming assistance. BTW, that 1/2 degree is about 1/110 radians, so (using the small-angle approximation for sine) the spot size has expanded to about 9m at 1km or 48 ft at 1 mile. Any convexity in the mirror will broaden the beam, at the expense of brightness | |
| Apr 28, 2017 at 22:16 | comment | added | Jamie Hanrahan | n.b.: My previous comment (3 hours ago) was in reply to a comment that is now apparently deleted. I'll take this op to add that if the reflection from the mirror was only the size of the mirror, or not much larger, aiming would have to be so precise that a signal mirror would never work at any appreciable distance. | |
| Apr 28, 2017 at 18:59 | comment | added | Jamie Hanrahan | Um, yes, there is such a thing in this case. Set up a mirror that bounces sunlight to a nearby building, then go look at the size of the reflection. You'll find it considerably larger than the mirror. The sun is about half a degree wide; it isn't a point source. | |
| Apr 28, 2017 at 14:43 | comment | added | Loduwijk | This is more of an answer addendum, but I did not notice it mentioned elsewhere. This is good to know and something I was concerned about. I was assuming it would be difficult to signal something far away, thinking it would require more accuracy in the angle, but now that I think about it, what you say makes sense. +1 | |
| Apr 28, 2017 at 12:33 | review | First posts | |||
| Apr 28, 2017 at 16:02 | |||||
| Apr 28, 2017 at 12:32 | history | answered | Andrew Davie | CC BY-SA 3.0 |