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> On Jan 2, 12:28pm, Chuck Taylor wrote:

>
> > The earth's axis completes one "wobble" in about 25,765 years. Besides
> > changing the location of the First Point of Aries with respect to the
> > stars, this phenomenon also has the effect of changing the pole star. In
> > 3,000 B.C. the pole star was Thuban. In 10,000 A.D. it will be Deneb. In
> > 14,000 A.D. it will be Vega, and in 23,000 A.D. it will be Thuban again.
> >

and Richard Edwards replied:
>
> I suppose for most of the time, there is no pole star.  That must make
> navigation a little more difficult.  When did Polarus become the pole star?

The following is quoted from "The Haven-Finding Art, A History of
Navigation from Odysseus to Captain Cook", by Professor E.G.R. Taylor,
Abelard-Schuman Limited, New York, 1957:

"... And the bright star at which the axis of rotation appears to end,
and round which the Bear wheels--the star we call the Pole Star--was in
Homer's day more than 12 degrees away from the pole, and did not attract
any particular notice. The nearest bright star to the celestial pole at
that period was the one now called Kochab, one of the so-called 'Guards'
in the Lesser Bear. Even so, Kochab was as much as 7 degrees away from
the 'nul point', and every year left it some seconds of arc farther off,
so that by A.D. 400 it was 10 degrees away, and the pole stood midway
between it and the modern Pole Star. But to an observer who makes no
measurements, and had no instruments, a star which actually circles
round the pole at a distance of even 7 or 8 degrees appears to be always
in the same place when he looks up at the sky. And it is reported that
even Eudoxus, the great founder of Greek astronomy, spoke of Kochab as
being always motionless, fixed at the pole of the universe. ..."

Bowditch (V.1, 1985) says that "By Columbus' time some navigators were
using Polaris to determine latitude...",  and later, "The north
celestial pole is moving closer to Polaris, which it will pass a a
distance of approximately 28' about the year 2102. Following this, the
polar distance will increase, and eventually other stars, in their turn,
will become the Pole Star."

That's as close as I can come to answering your question tonight,
without a trip to the library. Perhaps someone else can shed some
additional light on the subject.

Chuck Taylor
Everett, WA, USA
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