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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Fwd: Re: Sextant accuracy with short distance to horizon
From: Dan Hogan
Date: 2001 Jun 26, 3:13 PM
From: Dan Hogan
Date: 2001 Jun 26, 3:13 PM
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@EMC.COM Dan Hogan dhhogan@verionmail.com
