NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Silicon 84
From: George Huxtable
Date: 2002 Oct 19, 15:02 +0100
From: George Huxtable
Date: 2002 Oct 19, 15:02 +0100
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! ================= 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 ------------------------------ george@huxtable.u-net.com George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. Tel. 01865 820222 or (int.) +44 1865 820222. ------------------------------