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Alex Eremenko asked

>Can anyone explain me that the "Pointers" are?
>I mean this is something in the sky,
>probably a group of fixed stars.

Yes, these are the two stars at the working-end of the "Plough" (Ursa
Major), that point roughly toward the North Pole. They are alpha (or Dubhe)
and beta of Ursa Major. This indeed is common knowledge; every school-kid
ought to know it, but in Russia, no doubt, the name was different.

Beware, though, that in the 60 years that have elapsed since the paper Alex
refers to, precession has brought Polaris some 10 arc-minutes nearer to the
pole, so an allowance would have to be made to keep the result within the
claimed 4-minute error. The angle subtended at the pole, between the
pointers and Polaris, will also have changed somewhat from 135 degrees.

===========================

Things were more difficult in the great days of the Portuguese navigators
around 1500, when Polaris went round in a circle that was more than 3
degrees from the pole, so the correction was much more important to get
right (though I doubt that Columbus ever mastered it!).

In those days, the orientation of a line joining two stars known as "The
Guards" was used, both for telling the time at night and for correcting the
altitude of Polaris. The guards were beta (or "Kochab") and gamma of Ursa
Minor. If the line joining the guards was vertical, then the altitude of
Polaris was taken to be 90 degrees (which no longer applies). At other
times of the night it was corrected according to the slope of that line
between the Guards.

George.

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