NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Observations with pocket sextant in the Baltic
From: Alexandre Eremenko
Date: 2006 Jul 14, 02:52 -0500
Bill,
> Understood, it is the bias in that and other observations that concerns me.
> Lunars under, natural and artificial horizon observations under, Not by too
> much, 0.2' to 0.4', but there seem to be some systematic personal error.
I have something similar with my SNO, except that all my ovservations are
always "over". But again you do not cite specific numbers.
For example: 4SD under by 0.4' is normal,
but Lunars and art horizon Sun under by 0.4' is too much.
On the other hand, a Lunar under by 0.2' seems also normal,
because 0.2' seems to be on the boundary of possible accuracy for
one observations.
In my case, I am sure that this is not a personal error with
individual observations, but either some other error
(in the sense that I am missing something) or a sextant fault.
The reason is simple. I pre-set the sextant exactly to the computed
lunar or star distance for a given time, and then look.
And I clearly see that there is no touch, there is a visible
gap between the Moon and the star.
Of the things I could be possibly missing, determination of IC
is most suspicious. It is possible that the side error
(which I almost always have) distorts the IC measurements,
and as a consequence distorts all other observations.
Side error has indeed negligible effect on almost all angles
except very small ones, but now I realize that it can be very
relevant in measuring IC. Unfortunately, "Chauvenet on line"
is not readable from my computer (none of the web sites
suggested on this list) so I have to wait
till
my return to the US to check this conjecture.
I did not pay much attention to this in the past because of
the two reasons: a) Frank said that he does not care about
small side error and even leaves intentionaly some of it
"for convenience of star index checks", and
b) adjustment of the side error is extremelly annoying on
my SNO (and on other SNO's as reported on this list, and
on my pocket sextant) because the screw "plays back"
for the reasons that escape me.
> The last round my 4SD's were under by 0.3, 0.3, 0.2 and 0.2.
But these numbers indicate that your measurement of 4SD is
perfect!
> Less than 1/2.
Also seems normal to me.
Alex.
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From: Alexandre Eremenko
Date: 2006 Jul 14, 02:52 -0500
Bill,
> Understood, it is the bias in that and other observations that concerns me.
> Lunars under, natural and artificial horizon observations under, Not by too
> much, 0.2' to 0.4', but there seem to be some systematic personal error.
I have something similar with my SNO, except that all my ovservations are
always "over". But again you do not cite specific numbers.
For example: 4SD under by 0.4' is normal,
but Lunars and art horizon Sun under by 0.4' is too much.
On the other hand, a Lunar under by 0.2' seems also normal,
because 0.2' seems to be on the boundary of possible accuracy for
one observations.
In my case, I am sure that this is not a personal error with
individual observations, but either some other error
(in the sense that I am missing something) or a sextant fault.
The reason is simple. I pre-set the sextant exactly to the computed
lunar or star distance for a given time, and then look.
And I clearly see that there is no touch, there is a visible
gap between the Moon and the star.
Of the things I could be possibly missing, determination of IC
is most suspicious. It is possible that the side error
(which I almost always have) distorts the IC measurements,
and as a consequence distorts all other observations.
Side error has indeed negligible effect on almost all angles
except very small ones, but now I realize that it can be very
relevant in measuring IC. Unfortunately, "Chauvenet on line"
is not readable from my computer (none of the web sites
suggested on this list) so I have to wait
till
my return to the US to check this conjecture.
I did not pay much attention to this in the past because of
the two reasons: a) Frank said that he does not care about
small side error and even leaves intentionaly some of it
"for convenience of star index checks", and
b) adjustment of the side error is extremelly annoying on
my SNO (and on other SNO's as reported on this list, and
on my pocket sextant) because the screw "plays back"
for the reasons that escape me.
> The last round my 4SD's were under by 0.3, 0.3, 0.2 and 0.2.
But these numbers indicate that your measurement of 4SD is
perfect!
> Less than 1/2.
Also seems normal to me.
Alex.
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
