NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Precise index correction: was- Eye problems and IE, IC
From: George Huxtable
Date: 2006 Jul 14, 18:38 -0500
I had written-
| > Bill has told us that he obtains, consistently, a lower value for
4SD
| > (where SD = Sun semidiameter) from his observations of adjacent
Sun
| > images, than he would expect. I can suggest two reasons that ought
to
| > be at least taken into account, at the precision level he is
| > attempting to work to.
And Bill sounded a bit aggrieved (and perhaps justifiably so) in
replying-
| Unless I have totally lost it (the key word here being "totally") I
believe
| Alex and I have been discussing the merit or lack thereof over the
past few
| days of interpolating Almanac SD to more accurately reflect current
values.
| I believe I again addressed the problem of elevation in my summary
of stage
| 2 of tests your proposed, posted July 14, 2:08 EDT, 6:08 GMT.
|
| To quote me: "The experimenter cautions that the relationships
between
| vertical and horizontal measurement change as the body rises or
drops in
| relationship to the horizon. Therefore changes in elevation of the
body
| will affect the vertical to horizontal ratio. Care should be taken
when
| comparing observations taken at different times/elevations. The
experiment
| was designed to maintain body elevations in a region that minimize
these
| distortions."
Yes, I realised that Bill (and Alex) were aware of those
considerations, and perhaps I ought to have said so. What I really
wanted to emphasise was not just that these effects existed, but that-
1. The "rounding" problem could cause a significant offset,
consistently the same way over weeks at a time.
2. That considering the small perturbations that are being
investigated, local air-layer effects might be significant, if the
local weather wasn't aware of the standard refraction predictions.
It's fair to say, however, that at the high Sun altitudes that Bill
has been quoting in his recent observations, I would certainly not
expect to see any measurable distortion in its profile .
George.
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
From: George Huxtable
Date: 2006 Jul 14, 18:38 -0500
I had written-
| > Bill has told us that he obtains, consistently, a lower value for
4SD
| > (where SD = Sun semidiameter) from his observations of adjacent
Sun
| > images, than he would expect. I can suggest two reasons that ought
to
| > be at least taken into account, at the precision level he is
| > attempting to work to.
And Bill sounded a bit aggrieved (and perhaps justifiably so) in
replying-
| Unless I have totally lost it (the key word here being "totally") I
believe
| Alex and I have been discussing the merit or lack thereof over the
past few
| days of interpolating Almanac SD to more accurately reflect current
values.
| I believe I again addressed the problem of elevation in my summary
of stage
| 2 of tests your proposed, posted July 14, 2:08 EDT, 6:08 GMT.
|
| To quote me: "The experimenter cautions that the relationships
between
| vertical and horizontal measurement change as the body rises or
drops in
| relationship to the horizon. Therefore changes in elevation of the
body
| will affect the vertical to horizontal ratio. Care should be taken
when
| comparing observations taken at different times/elevations. The
experiment
| was designed to maintain body elevations in a region that minimize
these
| distortions."
Yes, I realised that Bill (and Alex) were aware of those
considerations, and perhaps I ought to have said so. What I really
wanted to emphasise was not just that these effects existed, but that-
1. The "rounding" problem could cause a significant offset,
consistently the same way over weeks at a time.
2. That considering the small perturbations that are being
investigated, local air-layer effects might be significant, if the
local weather wasn't aware of the standard refraction predictions.
It's fair to say, however, that at the high Sun altitudes that Bill
has been quoting in his recent observations, I would certainly not
expect to see any measurable distortion in its profile .
George.
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
