NavList:

Antoine Couëtte, you wrote:
"Hence we can safely consider that between H1 and H2, Standard Refraction is exactly linear."

Thank you for checking the explicit values. Good to know! How low would the altitude have to be before this would become a problem in a 20-minute interval (like the Venus sights in question)? And is there a way to manage it if we're concerned it's too low, and I want to be more careful but still use averaging? For example, if I correct both Venus sights and then average those corrected (Ho) altitudes, would that work better than averaging the raw sextant (Hs) altitudes? Seems like that would help. Or would it still be a problem?

You added:
"Preliminary Conclusion and implementation: good opportunity to use averaged Venus values here since their averaged time is almost exactly the Polaris observation time. Therefore no need to know about course and speed. In other words no need to use a running fix."

Yes, that's where I was going with this. It's a means to set aside any worries about a running fix, and of course, by doing two sights of the same body, we even reduce our error ellipse cross-section in that direction [not that this was a requirement of the puzzle --just thinking ahead here :) ].

You got a fix by the short method and a more complete running fix that agreed within 0.2 minutes of arc. That's re-assuring!!

You asked why I mentioned a 7x scope in the setup for the problem. Two reasons: 1) sometimes details are irrelevant to the basic solution of a puzzle and that's always worth remembering, 2) just as you say, there's a "center of light" issue. As Venus heads toward inferior conjunction in the next six weeks, its phase and size will matter more and more. Does the so-called "center of light" matter? Does it matter if you can't see it?? It's an intriguing question, and I don't think there's an easy answer to this. In fact, I believe it is magnification-dependent. I'll try to start a separate topic on this in a couple of hours. :)

Thanks for your input on this one!!

Frank Reed