Subject: Re: A Few Shots From South Africa
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.
> ...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.