NavList:

There's certainly room for disagreement here, but I've always taught my students to bring the body to the horizon in the same direction they measured Index Error.    If they measured IE by bringing the movable view of the horizon down to the fixed horizon, then they should also bring bodies down to the horizon, not up to it -- and vice versa.

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From: Thomas Sult <tsult@mac.com>
To: "NavList@fer3.com" <NavList@fer3.com>
Sent: Friday, August 17, 2012 3:46 PM
Subject: [NavList] Re: Swinging the Arc

The graphic is nice but shows the sun being brought down below the horizon and lifted. This would give backlash error.

Thomas A. Sult, MD
Sent from iPhone

On Aug 17, 2012, at 16:26, bill <billyrem42@earthlink.net> wrote:

> Indeed a nice graphic. It did appear the sextant was swung about the axis of the scope. I followed a link provided in the site to their sextant article
>
> http://en.wikipedia.org/wiki/Sextant
>
> which stated, " 'Swinging' the sextant about the axis of the telescope ensures that the reading is being taken with the instrument held vertically."
>
> This raises the old topic of whether the sextant should be swung about the axis of the scope, or axis of the observer to the body?
>
> If I recall the consensus was axis of observer to body. As I cannot walk and chew gum simultaneously, I have never quite figured out how to achieve that goal.
>
> I spent considerable time attempting the technique in my last round of observations from a pier on Lake Michigan using the Sun, Moon, Mars, Saturn and Spica. I did better on my very first beginner's round of sights using the home-built cardboard sextant from Celestaire from a 34' sailing craft!
>
> My intercepts from the pier ranged from 4!7'away for the Sun to 17'+ away for the Moon. Standard deviations were into multiple minutes, while my SD norm from land is 0!3 or less. On average, observations were an order of magnitude worse than my norm, and always away.
>
> So much for theory, at least as I practice it ;-)
>
> If anyone has a "Swinging the Arc for Dummies" article, I would love to read it.
>
> Bill B
>
>
> On 8/17/2012 3:45 PM, Hewitt wrote:
>> Here's a nice brief graphic of using the sextant. First one I've run
>> across showing things in motion.
>>
>> Hewitt
>>
>> Sent from my iPad
>>
>> Begin forwarded message:
>>
>>> *From:* Hewitt <hhew36@gmail.com <mailto:hhew36@gmail.com>>
>>> *Date:* August 17, 2012 12:31:23 PM PDT
>>> *To:* "hhew36@gmail.com <mailto:hhew36@gmail.com>" <hhew36@gmail.com
>>> <mailto:hhew36@gmail.com>>
>>> *Subject:* *File:Using sextant swing.gif - Wikipedia, the free
>>> encyclopedia*
>>>
>>> http://en.wikipedia.org/wiki/File:Using_sextant_swing.gif
>>>
>>>
>>> Sent from my iPad
>
>
>
>