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Re: Plumb-line horizon vs. geocentric horizon
From: Charles Seitz
Date: 2005 Feb 10, 08:46 -0500
From: Charles Seitz
Date: 2005 Feb 10, 08:46 -0500
Frank,
I must have a basic misunderstanding about how
a plumb line (the suspended weight) works.
My concept of gravity is that it is a force that orginates
from the center of mass of a body. On earth, that place
would be earth center regardless of the earth shape
model. If this is what happens, the plumb line should
extend to earth center.
If one considers a plane that is tangent at the
observer's location to the geoidal earth surface
and constructs a line perpendicular with the plane
there, this line would indeed miss earth center. I
would consider that line to define the local vertical.
With the exception of the poles and points on the
equator, it would not coincide with the direction
defined by a plumb line.
--- CHAS
----- Original Message -----From: Frank ReedSent: Thursday, February 10, 2005 03 44Subject: Re: Plumb-line horizon vs. geocentric horizonChas asked of a plumb-line in this context:"Is it a direction defined by a
plumb bob suspended from a cord or the
local vertical?"Yes and yes. Same thing. Also note that a still fluid will settle into a configuration where its surface is everywhere perpendicular to the local plumb-lines. This means that the local visible horizon at sea or on a large body of water or the surface of a pan of fluid as in an artificial horizon will make an excellent surrogate for the plumb-line.-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
