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Lu,

> I
> believe that there is well-documented evidence that the Portuguese were
> the first to produce declination tables decades if not a half-century
> before Columbus.

I believe that such table is present in Ptolemy's Almagest.
But I cannot check with my copy which is at home.
In any case Ptolemy perfectly understood how to compute declination table.

Assuming of course that the Sun rotates on an (excentric) circle.
That it is in fact an ellipse, is a later discovery, made more
than a century after
Henri the Navigator and after Columbus.

Of course I realize that seamen, even the most educated ones probably
did not read Ptolemy. And it is quite possible that the first tables
for seaman were made by the Portuguese.
By astronomers who certainly knew and used Ptolemy.

If I remember correctly, at the time of Columbus, the tables that were
available to navigators were the so-called Alphonsine tables
(first edition, 1583). They were updated and reprinted until
the better model of Sun motion was found by Kepler, which resulted
in Rudolphine tables (1627).

Alex.

   

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