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Subject: Re: Fwd: Re: Sextant accuracy with short distance to horizon
From: Dan Hogan (dhhogan@XXX.XXX)
Date: Tue Jun 26 2001 - 17:13:18 EDT
On 26 Jun 2001, at 16:49, Michael Wescott wrote:
> Dale Tilson wrote:
[Snip Aussie bit]
> >
> > OK, guys, I'm new at this so somebody help me out.
> >
> > I thought the "dip" correction was necessary because the horizon isn't
> > level with your height of eye. Aren't we actually trying to measure
> > altitude above a line horizontal with the line-of-sight? If so, our Aussie
> > friend would only need to find a perch so that his eye was level with the
> > fenceline.
>
> He'd need the fence to be level and to take his sights with the eye at the
> same height as the fence; in which case "dip" is 0. If either condition fails
> then the dip will be different depending on where on the fence the sight is
> brought down. That said, distance helps a lot. If the fence is 5 ft away, an
> inch off in the height of eye makes an error of about 58 minutes. At 20 ft
> it's 14' and at a half a mile it's 0.1'
>
> > If not, somebody straighten me out quick, because I was gonna set up an
> > observation post in the back yard based on that premise.
>
> You'll probably get better results with an artificial horizon. Say a pan
> of water or (my favorite) glycerin.
As much as I can remember, He owned what is called a "Station", the fence was
more than amile from his proch AND it was level, he had that part built on
purpose.
>
>
> --
> Mike Wescott
> Wescott_Mike@XXX.XXX
Dan Hogan
dhhogan@XXX.XXX
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