From: Whisky-dave <whisky.dave@gmail.com>
Subject: Re: A Few Shots From South Africa
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Date: Thu, 1 Mar 2018 08:33:57 -0800 (PST)
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Subject: Re: A Few Shots From South Africa
From: Whisky-dave <whisky.dave@gmail.com>
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On Thursday, 1 March 2018 13:47:41 UTC, -hh  wrote:
> 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. 

The apollos were 1960s technology too, well most that went to the moon were.

 

> > 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.

It does but it still won't see headlamps on the moon any more than it'll find the Spaghetti mosnster
on the moon.

> 
> >Out of 10^17 photons aimed at the reflector, ...
> 
> which is another way of saying ~0.25 Joules worth...

so not a lot then.

> 
> > only one is received back on Earth every few seconds, even under
> > good conditions.
> 
> Sure, but that's at the power level you specified. 

A power much higher than the aveage car headlight.
 
> 
> 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).  

Yes well aircraft don't fly at the same distance from the earth as the moon orbits.
> 
> Case in point, here's a 10W green Class4 for only $250:

I bet they can;t get that to reflect off something on the moon, and I bet such a laser if on the
moon couldn;t be seen from earth.

> 
> <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.

I didnl;t piuck any power level and it;s not really the power that is all important, at the distance
the moon is the small beam would be about 5 metres in diameter, spreading the light out.


> 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...

and how much the reflector has deterioded over that time.

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

So, it still won't be able to see the laser beam.
 
> 
> 
> -hh