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> Now I wish I hadn't.  Chapter 2 has several diagrams that are most
> upsetting.  They show a FLAT earth with a celestial object so close to
the
> earth surface as to suggest the difference in measured angle with the
> horizon (Ho) is due to the fact that the object's rays are approaching
at a
> different angle instead of the object's parallel rays hitting
different
> spots on the earth at different angles due to curved surface of the
earth
> (ignoring horizontal parallax for the moon).

My first introduction to celnav was a book that included a similar
diagram (I think it was of a tall street light), and it's served as
a useful mnemonic ever since to help me remember whether Ho>Hc means
"toward" or "away".  Yes, the mechanism is wrong, but I don't think
it hindered my understanding.  Does the book go on to show parallel
rays hitting a round earth later?

   

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