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As already explained by George Huxtable, the month to month variation in
the declination of Polaris is largely caused by the annual aberration.

Let's first examine the declination with respect to the true equator and
equinox of date *without* applying aberration. In the table below, the
first column of declinations shows a practically constant increase of
17″ per year. This is the effect of precession and nutation, that is,
the changing orientation of Earth's axis. (For some point elsewhere on
the celestial sphere the geometry could be quite different, possibly
resulting in very little change in declination during a year.)

In the second column of declinations I have applied annual aberration
but not precession and nutation. That is, Earth's axis is held fixed.
You can see a cyclic fluctuation, with Polaris returning to the same
place after one year.

The last column combines both effects. The values here essentially
duplicate the original posting.

             °  ′  ″     ′  ″     ′  ″
2006 05   +89 17 35   +17 34   +17 34
2006 06   +89 17 36   +17 24   +17 25
2006 07   +89 17 38   +17 17   +17 21
2006 08   +89 17 40   +17 15   +17 20
2006 09   +89 17 41   +17 18   +17 25
2006 10   +89 17 42   +17 25   +17 33
2006 11   +89 17 43   +17 35   +17 44
2006 12   +89 17 44   +17 45   +17 55
2007 01   +89 17 46   +17 53   +18 04
2007 02   +89 17 48   +17 55   +18 08
2007 03   +89 17 50   +17 52   +18 07
2007 04   +89 17 51   +17 44   +18 00
2007 05   +89 17 52   +17 34   +17 51

cfi@licfi.com wrote:
>
>  declination of polaris:
>  month        d   m
>  may         89.17.5
> june         89.17.4
> july         89.17.3
>  aug         89.17.3
> sept         89.17.4
>  oct         89.17.6
>  nov         89.17.7
>  dec         89.17.9
> -------2007------
>  jan         89.18.1
>  feb         89.18.1
>  mar         89.18.1
>  apr         89.18.0
>  may         89.17.8
> june         89.17.7
> july         89.17.6

I'm glad the question was asked. In the process of computing the table,
I realized my homemade positional astromomy software has no provision
for applying parallax. So I have a project to work on this weekend.
Fortunately, Polaris has a parallax of only .008 arc seconds.

Like all stars, Polaris also has "proper motion", a slow drift in its
position relative to a space-fixed coordinate system. My table does
include that, but it's too tiny to be apparent at 1 second precision.

   

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