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» Online Classroom   »   » Public Discussion of Cel Nav   » Refraction (again)

   
Author Topic: Refraction (again)
nfairfield


 - posted February 12, 2017 08:46 PM      Profile for nfairfield           Edit/Delete Post 
(Posting this with encouragement from David)

I have been greatly enjoying reading Emergency Navigation. For my own education, I've been comparing some of the memorization-oriented approximations with the tables in the 2017 Nautical Almanac.

In particular, I was looking at the approximation of refraction (pages 155-156 in the second edition). The plot starts the Low-angle refraction corrections at -34.5' (which is easy to remember). Looking at the A3 "Altitude Correction Tables 0 deg to 10 deg" at the front of the Almanac, it looks like the correction for zero degrees apparent is -33.8' (assuming nominal temperature and pressure).

After reading the (excellent) new/old blog post (http://davidburchnavigation.blogspot.com/2017/02/refraction-in-celestial-navigationstill.html) and looking at the Sinclair paper linked from the post, its clear that the difference is mostly due to "a more modern standard value" for the temperature lapse rate. It would be interesting to track down what changed -- or whether it was just a matter of a better measurement!

Thanks,
Nathaniel

From: MTV, CA


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