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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Old Style Lunar
From: Ken Muldrew
Date: 2005 Jan 11, 13:16 -0700
From: Ken Muldrew
Date: 2005 Jan 11, 13:16 -0700
On 11 Jan 2005 at 15:02, Frank Reed wrote: > "The airport elevation at Rocky Mountain House, Alberta is 3,242 feet." > > Which would decrease refraction values (absolute values) for all altitudes > below 45 degrees by more than a tenth of a minute of arc --and increasing > to 0.5 minutes of arc at 10 degrees altitude (10% of the standard sea > level values). Did Thompson correct for this? I don't think so, but his journals are just too devoid of details to know for sure. He always records temperature so I might be able to discover whether he takes that into account by re-doing one of his calculations where the temperature is quite extreme. > Most accounts of lunars were > written for observers at sea level, literally. Of course, if he measured > barometric pressure at all, I suppose it would necessarily have been with > a barometer calibrated at low altitude which would account for refraction > at mountain altitudes automatically (assuming he had tables that covered > such low pressures). There are some instances where he determines barometric pressure by measuring the boiling point of water, but only in high mountain passes. I doubt that he accounted for pressure elsewhere on his travels. I was just wondering if the apparent systematic error in his latitude data might be from neglecting the altitude. Ken Muldrew.