NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Refraction at the horizon.
From: Marcel Tschudin
Date: 2008 Mar 18, 12:20 +0200
From: Marcel Tschudin
Date: 2008 Mar 18, 12:20 +0200
George observed: > However, two of the observations were from Mauna Kea, Hawaii, at the great > height of 4205 metres, at which height much of the atmosphere has been left > behind. Based on the arguments above, one might expect to see the total > refraction significantly increased, with the extra refraction on the way up > being quite a large fraction of what it was on the way down. However, the > results show total refractions of 16' and 30'. Not good statistics, but > giving no support at all to the notion of a highly augmented total > refraction. > > In the case of Mauna Kea, the sea horizon is over 120 miles away, and less > than 30 miles of that path is over land, and that at significantly reduced > pressure. Would sunset times at that location therefore be expected to show > little fluctuation? The refractions shown for these two observations can really be questioned. With a standard atmosphere I would expect at this location rather refraction values somewhere around 50 min arc. Various calculations done so far indicate that super adiabatic lapse rates near the surface tend to reduce the total refraction. Looking at the soundings made near the time of those two observations: http://weather.uwyo.edu/cgi-bin/sounding?region=naconf&TYPE=TEXT%3ALIST&YEAR=1988&MONTH=11&FROM=3000&TO=3012&STNM=91285 and http://weather.uwyo.edu/cgi-bin/sounding?region=naconf&TYPE=TEXT%3ALIST&YEAR=1989&MONTH=01&FROM=2800&TO=2812&STNM=91285 indicate that the first of the two observations may have had (at least partially) such an influence. It would be interesting to hear how the observers explain those low refraction values. Marcel --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---