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    Re: Basics of computing sunrise/sunset
    From: Christian Scheele
    Date: 2009 Jun 18, 12:19 +0200

    Greg,
    
    thanks for your input. Right, one really has to keep an eye on those trig 
    functions which change sign going from one quadrant to the next. I was 
    assuming a dip of zero, which is not realistic but not too serious because I 
    often watch the sunset at the beach, sitting down almost at water's level.
    
    Christian
    
    
    ----- Original Message ----- 
    From: "Greg Rudzinski" 
    To: "NavList" 
    Sent: Thursday, June 18, 2009 1:41 AM
    Subject: [NavList 8683] Re: Basics of computing sunrise/sunset
    
    
    
    Christian,
    
    Even though the altitude is negative enter it into the formula as
    positive. Add the second part of the formula if latitude and
    declination are the same name(north or south) and subtract if
    contrary. Be sure to apply the equation of time in the correct
    direction and the same goes for the arc to time correction for the
    angular difference between the longitude of the observed sunset and
    the time zone meridian. If sunset is before 1800 LMT add 180� to the
    formula angle. If sunset is after 1800 LMT subtract the formula angle
    from 360�. Dip is also a factor to corrected for.
    
    Greg
    
    
    
    On Jun 17, 1:41 pm, "Christian Scheele"  wrote:
    > I'm trying to solve the following sunrise/sunset astronomical triangle and
    > am encountering unexpected pitfalls.
    >
    > cos(LHA) = [sin (a) - sin (lat) sin(dec)]/ cos(lat)cos(dec)
    >
    > where I am assuming a = -0.83 degrees
    >
    > It is of course something very basic and I'm almost embarassed to say that
    > although I keep rechecking what I'm doing, I remain with an error of about
    > 15 minutes by the time I get to the final result in mean zone time. Before 
    > I
    > drag everybody into it, could somebody please tell me whether there are 
    > any
    > snags that I should look out for?
    
    
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