Recent content by GeorgeHelio

The beam appears to fade more abruptly than one might expect because as the illuminated particles are ones further and further away the light intensity you see diminishes much faster than you will expect. The inverse square law is valid not only for the diverging laser beam outbound but for the...

If you set the above into Excel or other spread sheet, you can change the variables, of course, and discover what a difference the low dispersion angle makes. The above equations revealed that had we used just simple lighting that had a dispersion angle of, say, 65 degrees, then over 50,000...

Be careful what you wish for. Here is the method I used to calculate apparent magnitude (brightness) of our lighting. I had not references for this, so another method might be better. My hope was to be within one or two magnitudes (2.5x to 6.5x the actual brightness). [The green are the...

Thanks Jerry. It is fun to be here, and learn more about lasers. I suspect future ISS flashes or signals will be lasers only, though I don't want to discount the Sky-View search lights because they were the backbone of the flashing event. The laser idea was purchased for two reasons: the...

Hi Keith, I mean "Shooter"! :) I wish I could have been up the hill with you while you shot the station. The gun that Paul and Fred (from my work) had made, including a unique stand, needed you to have a little practice shooting since it had an off-axis pivot point. Unfortunately, you...

That's a great shot of Don in the Cupola! Here is a shot from Don showing some of the glare he talks about:

That might explain why my so called 445nm wavelength beam appears so blue. It is my limited understanding that 445nm is on the violet side of the blue-violet line. A 455nm beam would likely appear blue. [There is not definitive color chart that nails it for me, which may be due to the...

Wow, I didn't know green lasers required stages like this. Interesting. So a blue laser might have an "overall themral efficency" of roughly 22%. This seems to make perfect sense because maximum efficency is 683 lumens per watt, so at 22%, the efficacy for a blue laser becomes about 150...

This is confusing to me because the reason can be found in one of several corners. 1) Are we using input wattage into the diode for comparison? If so, then efficacy may be a big explanation for a green advantage over blue. Speaking of this, I guessed that the Arctic blue laser might be in...

This is my understanding, too. The cones are suprisingly broad in thei spectral receptivity. Peaks aren't the main thing to consider. I have been surprised by how often the peak points are used to argue issues about color. My specialty is heliochromology -- a term used to promote the odd...

At the risk of being too wordy, I would like to share things that may never get told. The story did go a bit viral, but I suspect by now it could be considered essentially dead, though Sky & Telescope may do something more elaborate. I will know more this weekend on this possibility. So, yes...

Thanks. It was a lot of fun, but after calculating that our lights should have been seen by Don as quite bright -- and I hoped that the ISS westward position would minimize glare -- that I was surprised that the arranged phone call did not take place. As it turned out, no phone call came...

That would help explain why my mag. values were a little higher than what Don Pettit reported. He said our light, including the brighter search lights, were seen as bright as a "mid Mars", which is probably between -1 and -2 mag., which is about 2 mag. dimmer than my calculations. That is very...

Nice thread (and forum)!! I was the number cruncher, whether they wanted one or not. It isn't that hard to calculate how bright an object will appear from space, once you see how to compare one standard (e.g. Sun) to whatever light we chose to use. [inverse square law and lumens per watt]...