# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Refraction:Which formula for Heights below 15°
From: Bela Kovacs
Date: 2022 May 18, 00:01 +0200
Herman:

I've attached a photo from this book (p. 280):
Sean E. Urban - P. Kenneth Seidelmann
"Explanatory Supplement to the Astronomical Almanac, 3rd Edition"

And I found an interesing PhD dissertation:

Wilson, Teresa, "Evaluating the Effectiveness of Current Atmospheric Refraction Models in Predicting
Sunrise and Sunset Times", Open Access Dissertation, Michigan Technological University, 2018.

https://digitalcommons.mtu.edu/etdr/697/

Regards,
Bela

Herman Dekker <NoReply_Dekker@fer3.com> ezt írta (időpont: 2022. máj. 16., H, 22:47):

Hello Navigators,

If the measured altitude (h) is <15° I learned in Franks  Advance Moderen Cel.Nav. Workshop:

I: R=1.0’/Tan [h+6.82/(h+4.024)]

In Henning Umland’s “A Short Guide to Cel.Nav.” the used formula is:

II: R=1.0’/Tan[h+7.31/(h+4.4)]

Can you explain the difference values?

If I calculated f.i. for h=0°,1°, 5° and 10° the calculated values are:

h=  0°      1°       5°     10°

I:  33.79’ 24.29’ 9.92’ 5.40’

II: 34.47’ 24.32’ 9.88’ 5.39’

The difference is negligible. but where come the different values in the formula from?

Regards.
HermanD

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