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From: Frank Reed (no email)
Date: Mon Jun 06 2005 - 22:53:21 EDT
George H, you wrote:
"The moment of LAN is delayed by 15.3 (tan lat - tan dec) * v where v is the
Southerly component of the speed in knots."
That adds needless complication to an otherwise extremely simple procedure.
And:
"It's worthwhile estimating in advance what this correction is going to be,
and in which direction, because what the observer is looking to measure is
the centre-of-symmetry of his plot of observed altitude. His observation
period ought to be 20 to 30 minutes before and after that moment of maximum
altitude."
Note that this adjustment is totally unnecessary using the simple procedure
that I outlined previously.
And:
"The whole object of the exercise is to discover the moment of noon. So how
does the observer know how many minutes each plotted point is away from
noon in order to calculate that adjustment?"
It makes no difference. Whatever point in time is picked as the "zero"
point, where no adjustment for northing/southing is made, will be the time of the
fix. Being able to label the fix as "noon" is not terribly important but it
is nicely traditional. The real time on it, of course, is a moment of GMT.
"However, it looks to me as if an error in
that initial presumption of noon would give rise to an error in the deduced
maximum altitude, and so in the latitude. Perhaps Frank will comment."
Nope. No error. See above. By the way, perhaps George could consider
addressing people in the second person. Thanks in advance.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
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