NavList:

Hello to all,

Let us make this puzzle easier to grab.

From a height of 310 m AMSL, with QFE = 983 mb and Temperature = 16.0°C, you have determined that your refracted sea horizon is at 31.2' below your local horizon.

You observe the Sun Center at 6.0' above this refracted sea horizon (vs. published value at 5.4'). The Sun horizontal parallax is 0.15'

From your DR position you have computed the geocentric Sun Center height to be at 63.1' under your same local horizon.

What is your intercept ?

Note : Obviously we are to deal with standard atmosphere here, even if in such case the standard refraction dispersion already reaches about 1 arc minute.

There can be situations when an intercept accurate to a few miles is better than no intercept at all.

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The usual sight reduction procedure is as follows:

(1) - Perform the DIP correction

Hence the Sun Center Height is at (31.2' - 6.0' ) = 25.2' under the local horizon.

(2) - Perform the Refraction correction

Obviously, no refraction tables exist for [invisible] heights under the horizon.

(3) - How can we get around this predicament, and derive some adequate estimate of the actual refraction of the Sun ?

Just use the Nautical Almanac refraction tables.

This is a simple, nonetheless challenging puzzle, worth studying.

Contributions expected this time :-)

Kermit