Let me quote the standard textbook: "American Practical Navigator, An Epitome of Navigation" originally by Nathaniel Bowditch, on dip with refraction. "The average value has not been established with certainty, and several methods of computing dip have been proposed. The values given in the critical tables on the inside front cover of the Nautical Almanac were computed by the equation D = 0.97 * sqrt h in feet....Minor discrepancies ... are not important in practical navigation."
I would add "and even less so in the design of sundials". Sunset phenomenon are not that precise. Roger Bailey Walking Shadow Designs N 51 W 115 At 09:35 AM 1/31/99 -0800, Slawomir K. Grzechnik wrote: >At 11:39 AM 1/31/99 +0100, you wrote: >>How about the dip angle which is there because your eye is not at ground >>level and the calculations think you are! >> >>Dipangle(in minutes of arc)=1.06*SQRT(ht in feet) >>Dipangle(in minutes of arc)=1.92*SQRT(ht in meters) > >Hi Thibaud > >Where did you get these formulae from? I have used for ages another one > >dip['] = 1.76 * sqrt( a[m] ) or its older equivalent >dip['] = 0.97 * sqrt( a[ft] ) > >where a is height of eye and units are given in bracket angles and ' stands >for minute of arc rather than foot. The formulae include Earth curvature >and mean terrestrial refraction for
