NavList:

Thank you for all your responses, I learnt much from them.

The answer to Frank’s last message deserves paraphrasing Dr. Watson’s memorable remark “You amaze me, Holmes! I mean, Reed!”  The sextant sights I posted were indeed taken around local noon on Saturday, November 16, 2019, which was a sunny, cool, and windy day on the Jersey shore. After recovering form my surprise, I reasoned that if one can calculate a position given date, time, and altitude, one might also be able calculate a date given position, time, and altitude. Still, it was very elegantly done!

I appreciated the different approaches proposed by Brad, David, and Frank, which rely on valuable pre-mid-20th century technology.  Curve fitting was impractical before the computer age, but the tracing paper method, which relies on visual alignment, was definitely available. My professional field (I am of retirement age but not completely retired) is vision - vision as in eyesight, not vision as in politics - so I find methods that rely on visual function very appealing.  I was pleased by the agreement between both techniques, even if this is a particularly favorable instance. In general, obtaining similar results with different approaches provides a useful sanity check.

Frank, David, and Igor clearly answered my question as to when and where the sun’s altitude as a function of time is approximately parabolic, and one can take advantage of this fact, and when it isn’t.  I probably have a middle latitudes bias, having always lived in them, and do not think enough about situations involving very low latitudes and very high latitudes.

Last, but definitely not least, I am very grateful for John’s warm welcome. I look forward to interacting with the NavList community in the future.

Kind regards,
Rafael