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    Re: A Ball Bearing in a dish as a reference
    From: Peter Monta
    Date: 2018 Jun 9, 23:41 -0700
    Hi Paul,

    Apparently no reflection was truly detected at Lick Observatory until
    August 1, though it was announced days earlier as the moonwalk came to a
    close. I have a DVD with the whole moonwalk, and the announcement from
    the "voice of Mission Control" is on the soundtrack. I don't know why it
    was premature.

    Yes, I came to the same conclusion.  The announcement during the moonwalk is definitely on the transcript, ascribed to "PAO" (public affairs office).


    I think the stated wavelength is a deep red color. The spot size on the
    Moon has been variously described as about 1 mile or 7 km. The pulses
    were on the order of a nanosecond even back in the day, so I doubt they
    would have been perceptible.

    Yes, 694 nm is very deep red and is on the exponential slope of the eye's sensitivity-loss further to the red.  Still, it is visible.  The pulses are short, yes, but from the standpoint of perceiving them by eye, it's the overall energy per pulse that counts.  If the complete pulse contains more than a few hundred photons (fewer with dark-adapted eyes, but the astronauts would not have been dark-adapted) focused on a few cone cells, that should be visible, even if the pulse is very short:  the neurons do not know that all the photons were deposited simultaneously.  Apparently early on they were using ruby lasers with rotating-mirror Q-switching, giving a pulse of about 4 ns.  Later during the 1970s the laser systems were changed to support narrower pulses.

    Unfortunately, I have not been able to locate the "first-person account
    of the project" mentioned at the bottom of the above article.

    It seems to be here:


    linked near the top of this page:


    A very entertaining and informal account!  It's certainly clear that nothing was seen on July 20 and for some days afterward.

    Cheers,
    Peter

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