Subject: Re: A Few Shots From South Africa
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:
....that's 20x the power level you picked, and its an off-the-shelf
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
Case in point: Nikon D5 goes up to ISO 3,280,000, which has 15x
the light sensitivity of classical old ISO 100 film.