NavList:

   

Reply

Ladies and Gentlemen:

I had another humbling night with the sextant on Friday.  I measured the
distance between Regulus and the far limb (east facing).  This on the
night of the full moon when the moon was more than 180� of GHA east of
the sun, so I think I was working with a fully illuminated limb.  While
I had some blurriness of the limb while making some of the contacts, I
felt reasonably confident.  You can see from the results that I still
had some scatter (+ - 1.0�), but taken together I got a reasonably
consistent set of sights for a beginner (ie, all sights were within 1.0'
of the best fit line).

Unfortunately, the bottom line was less pleasing. My distance yielded an
estimate of GMT 5 minutes 27 seconds ahead of GMT by GPS. Using Bruce's
method for translating that error in time to error in distance measured,
I was long by 3.4'. I went back out and reexamined a star-moon contact
and moved my arc back and forth 3.4', and it is a glaringly obvious
difference, I would not have missed it in taking the sights. So I begin
to suspect instrument error or some other systematic error. I worked the
calculations by two different methods, so I don't think they are the
problem, but would love it if they were.  I am curious if the full moon
in any way distorted my limb, but I think that is wishful thinking.
Please let me know if any of you find an explanation for this error.
More practice....

Time and position by GPS
Date:   3/29/02
Time            Ds
02:22:22        44� 19.8
02:25:16        44� 22.6
02:26:26        44� 21.8
02:28:02        44� 23.9
02:29:15        44� 23.0
02:30:37        44� 24.8
02:31:40        44� 23.8
02:33:03        44� 25.0
02:34:06        44� 25.5
02:35:18        44� 25.0
02:36:16        44� 26.4

DR Lat          42      22.7    N
DR Lon          71      9.9     W
Selected Time   2       30      0
I C                             -2.6    min

Body:   Regulus
GHA1            216�    18.3
GHA2            231�    20.8
Dec1            11�     57.4    N
Dec2            11�     57.4    N
SHA Star        207�    52.6
SD Sun          0

Body:   Moon
GHA1            22�     47
GHA2            37�     14.9
Dec1            0�      44.2    S
Dec2            1�      0.1     S
HP Moon         61.3    min

D1              43�     1.1
D2              43�     39.0
Delta / hr              37.9
Sc              59�     34.5
Sa              59�     35.1
Mc              33�     5.4
Ma              32�     15.0
Moon R&P                50.41
S R&P                   -0.59
Moon aSD                16.86
Ds              44�     24.0    at far limb
Da              44�     4.5
D               43�     23.5
GMT Obs 2:35:27
Dist Err                3.4'

More practice, more practice...

Regards,
Arthur

   

Reply