NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Refraction. was: Bubble Horizon Altitude Corrections
From: Richard B. Langley
Date: 2004 Jul 5, 23:25 -0300
From: Richard B. Langley
Date: 2004 Jul 5, 23:25 -0300
On Mon, 5 Jul 2004, George Huxtable wrote: >Fred Hebard has an inquiring mind, and a tendency to ask interesting >questions. The one copied below came to me off-list >George, > >A private question, which you could make public if you wish. Are there >ever events in the atmosphere where astronomical or distant earthly >objects will appear lower than they really are, rather than higher, ie. >events where the effective index of refraction is of opposite sign to >that usually encountered? By effective index of refraction, I am >trying to indicate the total refraction between the object and the >observer rather than a local refraction. >Atmospherics is not my specialty, though I'm as willing to pontificate >about it as the next man. I'm posting Fred's question to the list, in the >hope than someone will pick it up who knows more than I do. >The quick answer is: I don't know, but think it's very unlikely. * * * Just before reading that message, I read a message from another group to which I subscribe, the Sundial List. It's not related to an astronomical observation but is still interesting. I quote that message verbatim. -- Richard Langley Hello sundial lovers, this is a bit off topic, but the sort of thing some of you might enjoy. Working at the airport has its advantages. Just today, I saw the Queen's airplane arrive (security assures me the woman stepping out was NOT the Queen, nor was the other lady the Minister whom I - and the policemen - seemed to recognize). Another tourist attraction was the test flight with the 1948 vintage Constellation. What amused me - and the technicians who had the time to look - most was this. Although all runways have radio beacons, there are PAPI lights as well. While working on the antenna array of the localizer on a particular runway, traffic was starting in the opposite direction on that runway, i.e. away from us. Occasionaly, a heavy would come in to land. _That_ direction has no localizer, so the PAPI (Precision approach path indicator) lights were on, at full brilliance to fight the sun. We could just see them over the slight bluff, but whenever a plane started, the lights would disappear behind the bluff. Stepping on a car tyre brought the lights back; the difference was about half a meter! First I thought the hot air from the jets caused this, but later I realized that hot air would help makes the lights visible (go "up"), not invisible. It was the other way 'round. The hot air over the bluff was disturbed by starting aircraft, which would mix in vast amounts of cooler air from a few meters up, making the light rays go straighter. Then after a few minutes, the air would be hot enough again to bend the light from the PAPI lights over the bluff. Everyone I told found it hard to believe that this would be so strong an effect over just a few hundred meters. Most took pictures when they had looked and seen it for themselves! Rudolf 52-30'N 4-40'E - =============================================================================== Richard B. Langley E-mail: lang@unb.ca Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142 University of New Brunswick Fax: +1 506 453-4943 Fredericton, N.B., Canada E3B 5A3 Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/ ===============================================================================