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Subject: RE: [Nml] Early days of noon-sights...
From: Abel, Lu (Lu.Abel@XXX.XXX)
Date: Mon Jan 25 1999 - 12:29:32 EST
I don't know all the answers to Russel's questions, but let me at least
throw out a few comments on declination.
>From what I understand, beyond pure dead reckoning, navigators up through
about the mid-15th century had only Polaris sights as a source for latitude.
As most who have even cursorily read of the 15th Century voyages of
discovery, Prince Henry of Portugal (third son of the king, so not much to
do except be available in case his two older brothers died) early in the
century established the first scientific institute to study, advance, and
teach navigation. Some believe Columbus studied there at one point in his
career. The 15th Century equivalent of America's space program of the 1960s
was Portugal's determination to get to the Orient by sailing around the
bottom of Africa -- no mean feat, since at the beginning of the century
European knowledge of the coast of Africa extended only about 50 miles south
of the Mediterranean. The Portugese pushed steadily southward over the
century, finally passing the Cape of Good Hope at the end of it. While
there is no record of his actually been on a sea voyage, Henry the Navigator
pushed his scientists to solve the practical problems of navigation needed
for this exploration of Africa.
One of the major results was the first table of Sun declinations, worked up
by a couple of astronomers on Henry's staff about mid-century. And it was
none too soon, since the Portugese explorers were down to the equator and
it's darn hard to see Polaris from south of it :-). The declination tables
allowed the Portugese navigators to determine latitude without Polaris, and
allowed them to record and chart what they found south of the equator.
One thing I don't know is how soon declination tables spread to other
navigators -- navigational data (charts, sailing directions, and, I'm sure,
declination tables) were considered state secrets back then. I'll leave it
for some Columbus experts to say whether he might have had them.
Lu Abel
> -----Original Message-----
> From: Russell Sher [SMTP:rsher@XXX.XXX]
> Sent: Thursday, January 21, 1999 10:14 PM
> To: 'navigation@XXX.XXX'
> Subject: [Nml] Early days of noon-sights...
>
> I am curious to know; In the early days of parallel sailing and relying
> almost exclusively on the noon-sight, Where did early navigators obtain a
> table of declinations? Was this perpetual or was it renewed annually?
>
> Russell
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