Indeed. The Link A-12 sextant I have is shown on the page "Navigation
at War"
To take a reading, one rotates the plastic circular disk and puts the
object in the bubble. The markings are made on that disk as well.
At 12 o'clock, one can make out the "pencil" device that marks it. A
thumb activated mechanism moves the pencil to mark the disk.
On the left are the silver the battery compartment cylinder and the
illumination cylinder for the the bubble. Hidden in this picture are
the sun/haze filters and the movable "mirror" that changes angle as the
circular disk is rotated.
The main readout is in half degree increments. A vernier allows one to
read down to 1' of arc. One minute equates to one nautical mile of
longitude or latitude at the equator.
Woe be the navigator that doesn't erase all markings on the disks before
the next readings. Running out of pencil lead isn't recommended.
Brian
On 7/1/2013 16:04, Robert Atkinson wrote:
For those of us who would have to navigate a long way, there is a on-line
http://timeandnavigation.si.edu/
Robert G8RPI.
________________________________
From: Jim Lux <[email protected]>
To: Discussion of precise time and frequency measurement <[email protected]>
Sent: Monday, 1 July 2013, 13:56
Subject: [time-nuts] Smithsonian Time/Nav Exhibit
I had a chance to go through the Time and Navigation exhibit at the
National Air and Space Museum last week. From a "time" standpoint,
there's probably not much there that time-nuts don't know already, but
it's kind of cool to see cleaned up examples of equipment from days gone
by. (there's an old cesium beam from NIST on display, and a Symmetricom
cesium turned on and counting, but also a lot of old GPS stuff... lots
of Rb and Cs for space)
Quite a lot of the exhibit space was devoted to the problem of air
navigation, which, now that I've seen the exhibit, I can understand what
challenge it was. Over centuries, folks had figured out how to navigate
on ships and on land, but those are inherently slow moving, so you can
do things like take multiple sextant sights and reduce them.
But planes move fast, so you don't have as much time to do it. It took
real guts to be the navigator in the little cockpit out front of the
plane, taking sights with your body out in the wind. And the poor
fellow who was sucked out of a plane when taking sights standing on his
seat and the astrodome blew out.
It was interesting to see how many different schemes were used for
(mostly radio based) nav in airplanes over a fairly short time. Low
Frequency DF, A/N Ranges, VOR, LORAN, etc. I didn't see Omega.
They have an inertial nav unit there from a sub, but not much
explanation of how inertial nav works.
They talk about the DSN (and actually have a 4 bay rack of the old
time/frequency distribution gear on display), but not much discussion
on exactly how we do navigation for deep space.
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