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Russell Sher writes:
 > Here is some info. from Navigator Light which calculates Betelguese at each
 > of the times which you shot it. This confirms the (long) intercept which you
 > got. (e.g. first one is 87.9').
 > I used your AP for the DR input to the the program - (this should simulate
 > your exact calculations). There does not appear to be other of the 'primary
 > navigational stars' close to the Az or Alt which you got -- i.e. I think
 > that the star is correctly identified.
 > The only suggestion which I offer is: look up one of the 'secondary' stars
 > in the almanac and see whether one of them best fits your calculations.

As you can see, the simple explanations don't work.  You've confirmed
my results, acheived with both StarPilot and Celesticomp calculators.
I also tried their respective star ID programs to see if, as you
suggest, I was shooting something else.  Unfortunately, nothing turns
up.  Also, because Betelgeuse's appearance and location are pretty
hard to miss, I'm pretty sure that's the star I was shooting.  All of
Orion was visible and I chose Betelgeuse because it was the equivalent
of shooting at the broad side of a barn: hard to miss.  I set my
sextant back to 0-00 and brought the star's image down to the
horizon.  Since conditions were nearly calm with a 1' swell running, I
doubt I lost track of the star as I brought it down.

 > #1
 > Betelgeuse 08/22/2000 09:28:20 GMT
 > GHA:24�17.0'   Dec: 7�24.5'N
 > LHA: 309�37.0'
 > Hc:34�54.2'  Hs:34�55.6'  Az.calc: 111�
 >
 > #2
 > Betelgeuse 08/22/2000 09:29:34 GMT
 > GHA:24�35.5'   Dec: 7�24.5'N
 > LHA: 309�55.5'   RA: 5:55:11
 > Hc:35�07.6'  Hs:35�09.0'  Az.calc: 112�
 >
 > #3
 > Betelgeuse 08/22/2000 09:30:34 GMT
 > GHA:24�50.6'   Dec: 7�24.5'N
 > LHA: 310�10.6'   RA: 5:55:11
 > Hc:35�18.5'  Hs:35�19.8'  Az.calc: 112�
 > I have one question: what is the watch time which you refer to? (It is not a
 > whole hour differance to the UT ?? -- how did you get it?)

I've been timing my sights with a stopwatch.  I start it at a specific
time (in this case, 09:20 UTC, according to my notes) and then simply
note the stopwatch reading when I take the shot.  Later I convert that
to UTC and do the reduction.  Note that in the table I posted, I
re-started the watch at 09:49.  The watch loses about a second over
about 30 minutes so it's easier to just re-start it than to factor in
a rating as well as converting to UTC.

Because the Jupiter and Moon sights worked out (as well as sights at a
later date), I think it's safe to assume the sextant is properly
adjusted.  Again, watch time holds up well enough over about 10
minutes to give usable results for the latter two bodies.

So, what happened?  Whatever error I made is a consistent error, the
sights group reasonably well.  Later sights also group well and are
reasonably close.  The only possible explanation I'm left with is that
I consistently mis-read the sextant.  My point in raising this matter
is working out a reliable technique for locating the error.  Here's
why that matters.

Last weekend we took a 50 mile trip down the Chesapeake.  On my way
back north, I decided to do practice with sun lines even though land
was in sight and it's as easy to come up with a fix from landmarks as
to use sun lines.  I grabbed one line around 1300Z and the clouds
closed up tight until about 1700.  Now, let's assume I don't have the
familiar outlines of the Chesapeake in sight.  Instead I know that
St. Pomme de Terre is over the horizon somewhere and my DR's gotten
pretty shaky.  So here I am with the clouds opening and closing at
their own whims and all I've got is a flaky star line and two more
seemingly good lines and a single sun line of uncertain reliability.
Getting those Betelgeuse lines back looks mighty attractive!  [g]

Rick
S/V One With The Wind, Baba 35

   

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