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    Re: Visual Satellite Navigation
    From: Frank Reed
    Date: 2016 Jul 9, 22:36 -0700

    Robert II, you wrote:

    "And on that note, deciding that this thread has strayed at least 2 steps from navigation.  Returning to something akin to celestial nav, though only related, I see that there will be 2 Iridium flares at my house in the next 2 hours, one at -5.6 apparent magnitude, so very bright.

    Navigation by observation of visual satellites, however, is on-topic, albeit a little exotic. And this season, near the June solstice, is primetime in mid-northern latitudes. One can observe satellite passes over one hundred times in a single twilight period with a pair of binoculars and a good watch as your only required hardware. Each observation yields an error ellipse on the order of two miles wide and ten miles in length, and when a few dozen observations are combined can potentially fix your position within a quarter of a mile.

    For a practical case, last week I observed four satellite passes in ten minutes, and they were all two to four seconds ahead of schedule. That led me to wonder if the time on my smartphone was wrong. But three seconds off? That shouldn't happen in the year 2016. Digging around I eventually discovered that the device's time update functionality was turned off. The time error was, in fact, three seconds. Once network time updating was re-activated all of those satellites were back on schedule... I had effectively reset my "chronometer" by visual satellite observation.

    Back to Iridium flares, I expect that there is practical navigation information in observing these flares that has not yet been explored. The Iridium satellites orbit on a rigorous repeating schedule along certain longitudes of right ascension (equivalent to SHA) by design, and the flares occur in patterns like the glints from a diamond. Can we use these patterns? Anyone have any ideas?

    Frank Reed

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