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    Re: A Ball Bearing in a dish as a reference
    From: Peter Monta
    Date: 2018 Jun 9, 00:36 -0700

    Near the end of the moonwalk the announcer in Mission Control
    said, "The Lick Observatory in California reports a return on the laser

    That's quick work.  Was this at visible wavelengths?  Would the astronauts have been able to see anything if they were told when to look?  Of course they had a lot to do besides gawk, but on the other hand that's an opportunity that doesn't come along every day, to see an artificial light source from Earth with the naked eye at lunar distance.

    Speaking of spirit levels:  suppose an inexpensive 0.1-arcsec tiltmeter is desired (for a zenith camera).  Could bubble vials meet this, if the bubble were looked at with a camera and suitable signal processing applied to the bubble edge?  Assume the signal processing and mounting are ideal, so it's a question of the limits of the vial "physics package" (hysteresis, thermal issues, etc.).  The vials I have are 20 arcsec for 2 mm travel; the camera would have no trouble seeing 10 microns of bubble travel.


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