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    Re: Sine curve to approximate declination
    From: Trevor Kenchington
    Date: 2004 May 19, 21:13 +0000

    Frank Reed wrote:
    
    > A big part of this error results from the fact that the ecliptic only
    > looks like a sine curve. It's not a bad approximation, but the real
    > curve has "broader shoulders" than a sine curve. It's easy to see this
    > by imagining what the ecliptic would look like if the Earth's axis were
    > tilted, say, 80 degrees instead of 23.45.
    
    
    
    Frank,
    
    It may be easy for you to visualize that but I'm afraid I can't see it.
    I can visualize how things would be if the Earth's axis lay in the plane
    of the ecliptic (i.e. a 90 degree tilt), since that reduces to 2D
    geometry. But in that most extreme case, and assuming a perfectly
    circular orbit, I think declination would change linearly from solstice
    to equinox and vice versa -- meaning that the curve would have "narrower
    shoulders" than a sine curve.
    
    Can you explain how you see the "broader shoulders"? Or does the
    explanation lie in the departure from circularity of Earth's orbit?
    
    
    Trevor Kenchington
    
    
    --
    Trevor J. Kenchington PhD                         Gadus{at}iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
    
                         Science Serving the Fisheries
                          http://home.istar.ca/~gadus
    
    
    

       
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