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    Re: A Ball Bearing in a dish as a reference
    From: Frank Reed
    Date: 2018 Jun 13, 14:13 -0700

    You can, of course, look directly at a laser from great enough distance. Coherent light isn't brighter than other light.

    There was a fun experimental demo of this some years ago. An amateur astronomy group used searchlights to signal astronaut Don Pettit aboard the ISS. They also aimed a blue laser (800 mW) at the station, and Pettit was able to see both the searchlight flashes and the blue laser. Space stations are fun! Some details:

    I was surprised to learn at laserpointersafety.com that the "nominal ocular hazard distance" (in plainer words, the "low-risk quick peek" distance) for an 800 milliWatt blue laser is less than 500 feet, and the FAA glare distance is less than three nautical miles. I would have expected distances ten times greater...

    I do wonder if astronauts on the Moon could hypothetically see the laser pulses used for the laser-ranging experiments. Given that the beam spreads to about a kilometer at that range, I doubt that there would be anything visible under normal conditions even with the high-power focused beams used for laser-ranging. The beams surely wouldn't be bright enough to cause any eye damage at that range, right?

    Frank Reed

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