Please excuse what may be an off topic topic. Two things.... A while back I asked a question about an astronaut saying "hello" from the ISS using a signal mirror. Well what about the other way around? We can see flares (reflections of sunlight) from silver parts of satellites (not true mirrors), some even in a sunlit sky. Now, can anybody estimate how large of a rear-surface mirror would be needed by a person on the ground to effectively signal an observer on the ISS? Apparently the ISS windows are often (if not always) in a position to see such an event. I'm sure there are a number of variables to consider. For example: (1) The mirror would need to be in daylight which would position the moving ISS in a sunlit sky so it could not be seen directly, at least not at this time. (2) The ground itself---like the bright sky---would lower the contrast of the light so the bigger the mirror the better. This problem of contrast would limit any misalignment on the part of the astronaut doing the watching. Foveal vision might be necessary and is not large by any means. For example, off the Net: "While the normal field of vision for each eye is about 135 degrees vertically and about 160 degrees horizontally, only the fovea has the ability to perceive and send clear, sharply focused visual images to the brain. This foveal field of vision represents a small conical area of only about 1 degree." I know that if a daytime iridium flare is not within my foveal vision I often miss it. (3) It would be challenging to place a large mirror at an angle that would result in an acceptable alignment. One would NOT need to move the mirror during the event, just get it positioned accurately. [I can only imagine what the neighbors might think while watching me in my yard putting blocks of wood and whatever else I can come up with under a large mirror. Then to have me tell them, "Oh I'm just setting up to signal a guy on the Space Station."] :~) Mounting a shutter to make it blink would make it more obvious. In contrast to my usual way of thinking, the placement of the Station near the sun would be at an advantage rather than a disadvantage, correct? Now a question that I would like to get answered is, has any astronaut on any orbiting vehicle ever seen a "flare" from something manmade on the ground? From orbit w/o optical aid isn't it difficult to see evidence of man's existence at all? A sharp reflection then would be evidence of something artificial. The other thing.... How bright of an incandescent light (or laser) would a person in a dark area need to signal an observer on a high pass of the ISS? This would I'm sure depend upon the light pollution that the person is embedded in at the time. Again, a matter of contrast. Thanks and clear skies, Tom Iowa USA ..... ----------------------------------------------------------------- To unsubscribe from SeeSat-L, send a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@satobs.org List archived at http://www.satobs.org/seesat/seesatindex.html
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