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    Re: Maskelyne and his "able computers"
    From: George Huxtable
    Date: 2004 Sep 25, 11:31 +0100

    Frank Reed wrote, on 22 Sept.
    
    >Consider especially the case of Sun-Moon lunars tables. If you
    >stay in ecliptic coordinates, the calculation is very short since the Sun's
    >ecliptic latitude is zero. The lunar distance, LD, is calculated from the
    >difference in ecliptic longitude and latitude using the simple rule
    >  cos(LD) = cos(diff_longitude)*cos(diff_latitude)
    >With the stars and planets, the ecliptic latitudes are low enough that
    >certain approximations can be applied which also reduce the task of
    >computation.
    >Rotating to RA and Dec would lengthen the calculations quite a bit.
    
    In a reply, I copied that text but omitted the first two sentences, then
    objected that the "simple rule" would give inexact answers. But in the
    special case of the Sun and Moon, the Sun's ecliptic latitude is always
    zero (as near as dammit) as he said. As a result, Frank's simple rule is
    indeed correct, in the case of the Sun. What he wrote was clear enough, but
    I had (as he says) "missed the point". Sorry about jumping to confusions.
    
    George.
    
    ================================================================
    contact George Huxtable by email at george---.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ================================================================
    
    
    

       
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