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Subject: Re: Silicon 84
From: George Huxtable (george@XXX.XXX)
Date: Sat Oct 19 2002 - 10:02:14 EDT
Mike Burkes said, inter alia:
When shooting Polaris I noticed or inferred from navigation texts that
averaging several shots is not mentioned. On occasions I have experienced
increasing altitudes in the course of a Polaris session. Any feedback would
be appreciated and thanks much!
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Polaris is not at the the pole but a "large" fraction of a degree away, so
its altitude does vary. But not by more than about 12 arc-minutes in an
hour, at its greatest, increasing, or decreasing. In addition, any
Northward or Southward component of ship's velocity would provide an
additional change of Polaris altitude of, say, 7 arc-minutes per hour, if
the speed of the vessel were 7 knots. Even if these were to add, this would
cause Polaris altitude to change by only 19 arc-minutes per hour, or 1 arc
minute in about 3 minutes of time. This slowly changing altitude would not
be very obvious to an observer unless the series of measurements was rather
prolonged. So how long was the "Polaris session" that Mike refers to, and
how much "increasing altitude" did he see? And what was the speed of his
vessel?
George Huxtable
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george@XXX.XXX
George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
Tel. 01865 820222 or (int.) +44 1865 820222.
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