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Re: Instrument for solving spheric al triangles
From: Patrick Goold
Date: 2012 Apr 26, 14:51 -0400
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Patrick Goold
Department of Philosophy
Virginia Wesleyan College
Norfolk, VA 23502
757 455 3357
From: Patrick Goold
Date: 2012 Apr 26, 14:51 -0400
Concerning the plural of astrolabe, I would suggest that astrolabes is best. Neither the OED nor the American Heritage give a plural form, suggesting that it is pluralized in the ordinary way by adding s.
Patrick
On Thu, Apr 26, 2012 at 1:57 PM, Alexandre E Eremenko <eremenko@math.purdue.edu> wrote:
Wolfgang,
As Geoffrey said there is a whole family of instruments
basically representing the celestial and the horizon sphere on
semi circles and circles.
I include to this family star globes and astrolabias (..ae?)
Not the Marine astrolabias, but of another type, which were
popular in the Muslim world...
They were first proposed in the 16th century
I suppopse these astrolabias were proposed in antiquity, Hellenistic
times, Ptolemy mentions them, but probably none survived.
Theit function was exactly the same as of all those
analog calculators, to give you altitude and asimuth
(and rasing/setting times and points, and culminations)
from SHA, declination and time).
By solving a spherical triangle using the metal divided circles,
which rotate with respect to each other.
My globe does this very well to 1 degree.
Applying very fine pivots and arcs and verniers you can probably
approach sextant accuracy on the devices of the same size,
but this is much harder to make than a sextant.
Alex.
Patrick Goold
Department of Philosophy
Virginia Wesleyan College
Norfolk, VA 23502
757 455 3357