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    Re: Automated Sun detector
    From: Mike L
    Date: 2007 Dec 7, 05:26 -0800

    On Dec 6, 6:43 pm, frankr...{at}HistoricalAtlas.net wrote:
    > "I've come to the conclusion that the only way to get any information on the
    > probability of seeing a sunrise/set is to build myself a sun detector and I
    > would like to post my idea to get some feedback."
    > Ok, here's some feedback: buy an alarm clock, a pencil, and a notebook.
    > Seriously, you are talking about the simplest astronomical observation that
    > exists. Set your alarm clock for the time of sunrise, get up and walk to the
    > window. See Sun? Put a mark in the notebook. I suggest a letter 'S'. Can't
    > see Sun? Put a different mark in the notebook, perhaps a letter 'N'. You can
    > expand on this system as time and interest permit... What you really need
    > are some students. Assign it to them as a year-long project. Then you can
    > sleep in. 
    the idea of going to the window sounds deceptively simple - if you
    happen to live in a cottage on the top of a hill in the middle of an
    island and don't have kids to get to school, journey to work etc.
    This morning it happened that the sun finally came out from beneath
    the blanket of cloud. Or at least I thought it had, as when I finally
    got somewhere where I could see it, I could hardly make out the
    outline of the sun, and in anycase it was probably 5degrees above the
    horizon or about an order of magnitude easier to spot.
    To update you, I've finally discovered that most solar detectors are
    horizontal and flat, and even if someone were to have minute by minute
    (or even 5min) sunshine figures, and even if they have a good view of
    the horizon, the figures will be entirely inaccurate and unlikely to
    differentiate between diffuse light scattered from above and the very
    weak direct light from the sun.
    All in all, this measurement is really beginning to drive me potty, as
    I can't even put an order of magnitude probablility on it except to
    say it is going to be less than 15% and perhaps as low as 0.005%.
    The problem is, that like most people, I've never set out to look for
    the sun at that moment it hits the horizon, and although I've seen the
    sun around sunrise/set, I've no idea how this chance observation
    relates to seeing the sun as it hits/leaves the horizon. As you say,
    it may be the only way is to wait until sunrise falls outside the
    "social window" of a family and spend a few months trudging up a hill
    to watch the non-appearance of the sun!
    > Kidding aside, I agree with Marcel that there is plenty of data available
    > already. At minimum, you can rule out sunrise visibility when the sky cover
    > is listed as 'overcast' or 'fog'. If you throw in some observational data of
    > your own, you ought to be able to estimate a probability of sunrise/sunset
    > visibility when conditions are 'mostly cloudy' and 'partly cloudy'.
    >  -FER
    Oh .... you were kidding! Grrrrrrrrrrrr ... a grinding and a gnashing
    of teeth is heard!
    But seriously, it is helpful having comments, even the obvious ones,
    as at least one sent me down a possible avenue, which although it
    turned into a blind alley, it did open up another blind alley, which
    had a very small chink of light coming from under a gate, which I
    could have sworn was sunlight - except it probably wasn't!
    One approach I considered was simply to assume that because you need
    an absolutely massive window in the sky to see the sun at sunrise/set
    this infers, that the only time the sun could be seen was during
    "clear sky" periods - or more accurately - whether some location
    50-100 miles toward the sun had a clear sky!
    Another approach, I've considered is buying a cheap digital camera,
    sticking it on a very long pole (5m!) above our house, and trying to
    find a timer that will trigger it to take pictures every minute or so
    around sunrise (I'd need another for sunset) - but I've no idea
    whether I could just rewire the trigger on one of these cheap cameras,
    or whether it would turn itself off and refuse to do anything!
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