NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Determining Actual Time of Meridian Passages Before Computers
From: Greg R_
Date: 2007 Jan 13, 14:53 -0800
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From: Greg R_
Date: 2007 Jan 13, 14:53 -0800
This got my curiosity up last week, and thought
I'd toss it out to the list for comments. I realize that it's pretty much a
no-brainer in this modern day of computerized calculations and
computer-controlled telescopes and the like, but how was it done in years past?
My best first-guess for a method of doing it
would be something like establishing a true north-south line (probably with a
Polaris shot and surveying gear) to establish the direction of the meridian,
then leveling and locking some sort of viewing device (maybe with crosshairs on
the boresight?) on that line so that it could only move in a vertical arc (i.e.
horizontal movement would be locked on the meridian line). Then some sort
of reasonably-precise timepiece (chronometer, etc.) could be used to verify the
actual time of meridian passage for a celestial object (obviously excluding the
sun in this example, unless shades were available on the viewing
device).
Does anyone know how it really was done back
then? Also, does anyone know what (if anything) is done in this modern age to
verify the almanac meridian passage times, or are the computer calculations so
accurate that they don't need to be verified?
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Thanks,
GregR
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