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    Lunar laser eye safety
    From: Paul Hirose
    Date: 2018 Jun 14, 16:54 -0700

    The Lick Observatory laser utilized on the night of the Apollo 11
    moonwalk emitted 8 Joules per pulse and the spot diameter was "about two
    Let us assume spot diameter = 3000 m. Then area = 7.1e6 square meters,
    and power density = 1.1e-6 J/m2, or 1.1e-10 J/cm2.
    An article in Wikipedia includes a graph "Maximum permissible exposure
    (MPE) at the cornea for a collimated laser beam according to IEC 60825,
    as energy density versus exposure time for various wavelengths."
    For pulses 1 ns to 10 us (the Lick laser was in that range), the MPE is
    6e-7 J/cm2, about 6000 times greater than the figure I calculated above.
    Perhaps that's applicable to repetitive pulses if the duty cycle is very
    small, like those transmitted from Lick. I'm not sure, though.
    According the PDF above, it didn't matter since the beam was aimed at
    the wrong part of the Moon! On the phone call between the Lick and
    Houston, "fifteen" arc seconds in the landing site latitude was copied
    as "fifty" at Lick.
    But unless I miscalculate, that would not be a serious error. On the
    Moon, 35 seconds of latitude is about .3 km. If the spot radius is 1.5
    km, the landing site should still be in the beam — ?

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