Star Magnitude Query

[GeeKay]

I understand from Wikipedia that the apparent magnitude of the Sun, as viewed from Earth orbit, is about -24.74. This being so, and allowing for the well-known fact that one would risk permanent eye damage by staring up at the Sun for any length of time (other than during sunrise and sunset), would it be possible to safely gaze at a point source of light if it were shining at a magnitude of -17? I gather this magnitude is around a hundred times brighter than that of the Full Moon, but still extremely dim by Solar standards. Nevertheless, as anyone who has had a 40 lux LED dynamo lamp directed straight into one's eyes (my lamp and my eyes, as it happens) they will know just how squintingly bright modern bicycle lighting can be. Therefore, I'm left wondering whether the same effect would apply to a starlike object with the above luminosity, namely -17 mag. I really would welcome any suggestions to help me over this baffling question.

[imatfaal]

Not sure on the light problem re stars - but will say that a 40 lumen led is pretty dim by modern standards. I ride with a 300 on the bars and 550 on my head when going on unlit paths at night - and whilst these will leave purple whorls in your eyes if you look directly for even a second they do not carry massive health warnings like a small laser pointer does.

 

edit

 

just realised your OP say lux not lumens - whoops! Sorry

Edited November 8, 2013 by imatfaal
retraction

[Amanbir Singh Grewal]

lumens is intensity or flux.

[imatfaal]

lumens is intensity or flux.

intensity is not the same as flux. the SI unit of luminous intensity is the Candela - one candela covering a steradian is a lumen. a lux is a lumen per square metre.

 

http://en.wikipedia.org/wiki/Candela

http://en.wikipedia.org/wiki/Lumen

http://en.wikipedia.org/wiki/Lux

[John Cuthber]

Sorry, I must have missed something,

Where did the number 17 in the OP come from?

[GeeKay]

Well, I'm also a bit uncertain about what flows from the differences between lux and lumens etc. I also gather that measuring light intensity is still fraught with unresolved problems, or at least ambiguities. Still, my B&M senso front light certainly slings out a lot of photons, however one counts 'em. My question is what happens on a much larger scale when all that intensity is squeezed (if that's the right word) into a narrow beam of light, one exhibiting no visible disc of any kind. I accept that any -17 magnitude starlike light source is beyond our human experience. Venus at -4.4 mag is the brightest natural object of this type we have in the heavens, and staring up at that certainly doesn't cause the eyes to water! And so, trying to apply this line of thought to a starlike object many times brighter than Venus is always going to be exceedingly difficult to imagine. What about the Moon then? If a star were as bright as the Full Moon (-12.5 mag approx), would that be hard to look at directly? Many thanks.