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    Re: Position from a photo
    From: Frank Reed
    Date: 2013 Jan 7, 13:14 -0800

    Ok, since this is for fiction, you might consider adding a fictional astronomical event. As long as it's consistent with similar astronomical events, that wouldn't be too much of a deus ex machina solution, or would it?

    Do you remember Comet Hayakutake in 1996? It was just spectacular under a dark sky. I was living in Chicago, and I borrowed a friend's car to go out to dark skies west of the city. While on the highway and getting further from city lights, I opened the car's roof hatch and it was the most beautiful comet I had ever seen, the tail stretching some 40 degrees across the sky near the North Star. I nearly drove off the road. The center was as bright as Arcturus and it was moving across the celestial sphere at approximately 1' per minute of time, double the Moon's rate. Photographs of its position taken in 1996, can be used to determine GMT to within ten seconds or better. Now that comet passed about 10 million miles from Earth. If you invent a fictional comet and let it pass at 2 million miles, with the same speed relative to the Earth, its apparent angular speed would be five times higher, and you could get GMT within two seconds. Such a comet would only be visible for a few nights, but that would make it all the more exciting. Maybe it could be "Comet Wassermann, known in Britain as 'Hitler's Damn Comet', some feared it would destroy the Earth in the middle of this terrible war... etc., etc." :) In a photo taken in twilight, it would appear as a slightly fuzzy bright star with just a hint of a tail. Perhaps its cometary nature would only be apparent when examined carefully with a magnifying glass... or something like that. You would still need some Sun altitudes for latitude and local time. I think it was Bill B. who suggested using Ken Gebhart's method here of estimating the Sun's altitude by the flattening of the image as it's rising or setting. That might work. Or maybe a photo of a low altitude Sun reflected in a still bowl of water...


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