NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Moon altitude problems.
From: George Huxtable
Date: 2006 Aug 22, 18:39 -0500
Robert Eno has lindly sent me, off-list, the original data, taken with
a bubble attachment to his sextant, on which his conclusions about
errors in observing the Moon were based.
I can confirm that my own analysis gives the following results-
Four observations of Vega; The recorded altitudes were lower than they
theoretically should have been, by 2.7, 0.3, 0.2, 1.9 arc-minutes.
Four observations of the Moon. The recorded altitudes were lower than
they theoretically should have been by 4.0, 4.5, 4.4, and 3.8
arc-minutes.
There isn't enough data here on which to base a proper statistical
analysis, but we can guess at a few conclusions-
In skilled hands, such a bubble attachment is capable of giving
remarkably good results; much better than I had expected, anyway.
Robert Eno is indeed making his corrections properly (or at least, in
the same way that I am).
The Vega data indicates that there's an "index error" of the bubble -
sextant combination, in which it tends to read low by a bit more than
1 arc-minute.
The Moon data shows up an additional error, in which the sextant reads
lower still, by about an additional 3 minutes. In the light of our
previous discussion, it seems to me that this could well be attributed
to the problems of centring an asymmetric Moon within the bubble, when
there's only half the circumference of the Moon available for use. I
see no need to call in aid any presumed defects in the Moon as an
observable object, based on ancient-mariners' folk-wisdom, but others
may take a different view.
George.
contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
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To , send email to NavList-@fer3.com
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From: George Huxtable
Date: 2006 Aug 22, 18:39 -0500
Robert Eno has lindly sent me, off-list, the original data, taken with
a bubble attachment to his sextant, on which his conclusions about
errors in observing the Moon were based.
I can confirm that my own analysis gives the following results-
Four observations of Vega; The recorded altitudes were lower than they
theoretically should have been, by 2.7, 0.3, 0.2, 1.9 arc-minutes.
Four observations of the Moon. The recorded altitudes were lower than
they theoretically should have been by 4.0, 4.5, 4.4, and 3.8
arc-minutes.
There isn't enough data here on which to base a proper statistical
analysis, but we can guess at a few conclusions-
In skilled hands, such a bubble attachment is capable of giving
remarkably good results; much better than I had expected, anyway.
Robert Eno is indeed making his corrections properly (or at least, in
the same way that I am).
The Vega data indicates that there's an "index error" of the bubble -
sextant combination, in which it tends to read low by a bit more than
1 arc-minute.
The Moon data shows up an additional error, in which the sextant reads
lower still, by about an additional 3 minutes. In the light of our
previous discussion, it seems to me that this could well be attributed
to the problems of centring an asymmetric Moon within the bubble, when
there's only half the circumference of the Moon available for use. I
see no need to call in aid any presumed defects in the Moon as an
observable object, based on ancient-mariners' folk-wisdom, but others
may take a different view.
George.
contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
