Subject: Re: A Few Shots From South Africa
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Date: Thu, 1 Mar 2018 05:47:29 -0800 (PST)
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Subject: Re: A Few Shots From South Africa
From: -hh <recscuba_google@huntzinger.com>
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On Thursday, March 1, 2018 at 7:19:12 AM UTC-5, Whisky-dave wrote:
> On Thursday, 1 March 2018 11:17:52 UTC, -hh  wrote:
> > On Thursday, March 1, 2018 at 5:33:38 AM UTC-5, Whisky-dave wrote:
> > > [...]
> > > Can you tell me which apollo mission (or any other) that 
> > > took car headlights to the moon. ?
> > 
> > Actually, they did take a corner reflector up there (at least once),
> > so headlights on Earth which happen to shine light that way would
> > have a direct path reflected back to Earth.  
> 
> There's no headlight on earth that could do that, what they left 
> there was for a laser to be shone to measure the distance to the
> moon oer time.

True, it was for a laser (which is light), but it was also designed
in the 1960s using 1960s technology for the receive sensor.  

> There;s no way a headlamp would be bright enough or be able to
> produce a beam bright enough to reach the moon and reflect back,
> it's difficult enough with a high power laser who beam only reflects
> back a very small amount of light in fact the reflected light is
> too weak to see with the human eye. 

Human eye?  Oh, sorry:  I thought this was about the ability of a
machine (Hubble's replacement) to have adequate senor resolution.

>Out of 10^17 photons aimed at the reflector, ...

which is another way of saying ~0.25 Joules worth...

> only one is received back on Earth every few seconds, even under
> good conditions.

Sure, but that's at the power level you specified.  

In contrast, Class4 laser today (minimum of 500mW) sell for as
little as $100 today, and 2W & 5W versions are pretty commonplace
(and why they're such a safety threat to aviation).  

Case in point, here's a 10W green Class4 for only $250:

<http://www.everyonetobuy.com/green-10000mw-burning-laser-pointer-pe...

....that's 20x the power level you picked, and its an off-the-shelf 
commercial product.

Plus we can similarly look at the sensor side, to see how much that
technology to detect the return signal has improved over the last
50 years...

Case in point:  Nikon D5 goes up to ISO 3,280,000, which has 15x 
the light sensitivity of classical old ISO 100 film.  


-hh