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Subject: 05-10+11 Lunars + scope adjustment
From: Fred Hebard (Fred@XXX.XXX)
Date: Fri May 09 2003 - 15:26:47 EDT
Doug,
Regarding the alignment telescope. This procedure is described also in
Bowditch, without the wires. Again, Bowditch says to chose two stars
at least 90 degrees apart and to note the angle, but no further mention
is made regarding use of that angle. I presume then that one notes the
angle to be sure it is at least 90 degrees. Perhaps others have more
knowledge of this?
One would bring the stars into confluence at one wire, and then check
that they are still in confluence at the other wire. Without the
wires, Bowditch says to bring two stars into confluence at one side of
the scope and then move them to the other side to check that they
retain confluence. Whether they separate or overlap would then tell
one in which direction to adjust a scope that was out of alignment. I
don't think modern sextants have provision for making this adjustment
in the field.
The wires may originally have had another use. Similar wires used to
be located in land-based astronomical telescope eyepieces. One would
note the time when celestial objects crossed each wire, to better
compute ephemerides and such. This may also have been the original
purpose of the sextant wires, for land-based observations using an
artificial horizon. Perhaps others can enlighten us as to the purpose
of the wires.
Simex or Takizawa, sextants have alignment scopes with two wires.
Fred
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