[time-nuts] Smithsonian Time/Nav Exhibit

Brian Alsop alsopb at nc.rr.com
Mon Jul 1 13:01:59 EDT 2013


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 <jimlux at earthlink.net>
> To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
> 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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