There are values for the real dip and the apparant dip (this is the one we see). The apparant dip = 0.92 * real dip
That explains exactly the difference. My formulas were apparently the 'real dip' formulas which I found in one of my books. >>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 > >standard pressure 760 mm Hg (1013.2 mb or hP) >air temp. +10 C >water temp. +10 C (guess formulae may be used on land as well) > >The result should be corrected for temperatures and pressure if you are >able to measure those, not that hard after all. "My" formulae are cited in >manuals of navigation and Alamanachs together with tables and correction >tables for temperatures and pressure. So where did you get "yours" from? > >Regards > >Slawek > >P.S. The so called terrestrial refraction refers to light rays arriving at >low altitudes that is close to the horizon. Refraction for high altitudes >is called astronomical. Physically this is the same phenomenon of bending >of light rays passing through the atmosphere. Close to the horizon however >air is "thicker" and influence of ground/sea and temperature differences is >significant. In special conditions terrestrial refraction enables you to >see really distant objects, sometimes inverted, and not only at Sahara. >Both types of refraction have to be taken into account for sextant >observations where celestial bodies are usually at high altitudes and >apparent horizon is at low (and negative) altitudes. > >Slawek Grzechnik >32 57.4'N 117 08.8'W >http://home.san.rr.com/slawek > ----------------------------------------------------------------- Thibaud Taudin-Chabot, home email: [EMAIL PROTECTED] (attachments max 500kB, in case of larger attachments contact me)
