NavList:

Hello All.

First of all I want to thanks all of you guys (David, Al) for your awesome explanations. I'm very much impressed by the quality of the discussions on this forum and the by time you take to help others. As I mentionned earlier, I've been working for decades in engineering, a field of work that has degraded a lot lately. Nowaday, science is not what it used to be. I'm glad to see people on a forum such as this one so dedicated to the science of celestial navigation. It's fairly new for me, but it is changing the way I see the sky and, I should say, the world. Stars and planets that I used to barely see up above my head are now acquaintances.

Now, regarding my problem, with all of your explanations, I come to the conclusion that the difference between my results is due to the inherent precision of each method. Nothing really wrong with the process.

Method 1. Using the Almanach's sunrise time and HO-249: Sunrise time is not what I expected it to be. If I'm not mistaken, the almanach considers the sunrise as the moment the upper limb hit the horizon, not the center of the sun. It would explain the error. Adding this time to the time it takes for the sun to climb half its diameter seems to solve the problem.

Method 2. The slight inacuracy of this method seems to be the result of rounding

Method 3. Seems to be the most accurate method. 

Again, thanks for helping me with this. I will certainly sleep better tonight (unless I end up looking at the sky all night :-)

Francois