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Good Evening, Patrick -

The first thing I did was to run your signts on my StarPilot hand
calculator using the lat/lon of your deck to get an idea of how the
sextant readings were going.

1) In the 1621 sight at first go it looked like you might have taken
an upper limb sight instead of the lower you indicated. Changing the
input to upper limb, the SP gave an intercept of 1.7' T.  So nothing
terribly awry with your sextant work.

Running the 1621 sight from the assumed position gave and intercept of
10.3' T. Since your assumed latitude is 10NM north of your deck, this
makes sense.

2)  For the 1718 sight the SP calculator gave an intercept from the
deck of 0.9' T. Real good!

From the assumed position, SP gave an interdept of 10.7' T. Again,
sensible given the distance of the AP from your deck.

3) For the 1842 sight the calculator gave an intercept from the deck
of 0.2'. Bravo!

From the AP the calculator gave and intercept of 10.7' T. Again,
consistent with the fact that you AP is 10 NM north of your shooting
position.

All in all, I'd say you've got the hang of things.

Hewitt



On 1/30/11, Fred Hebard  wrote:
> Patrick,
>
> I'm glad to hear that tectonic forces are not too aggressive in the
> vicinity of your garden.  I'm at about the same latitude, but 81* 50'
> W, and found out the same thing about the deck attached to the back
> of my house, much to relief of my family!
>
> I didn't work through all your sheet, but your assumed longitude for
> the first sight is 76* 7.2' W when the GHA would suggest that 62* 7.2
> W is correct.
>
> I started out with HO 229, but then moved to computerized reduction
> to focus on my sextant technique.  By the time I had the technique
> down, I was too lazy to go back to hand calculations!
>
> One thing I did find was that accurate timing, to the second, is
> critical. I used the difference between the observed altitude and the
> calculated altitude as a metric of accuracy.
>
> Fred
>
>
> On Jan 30, 2011, at 7:40 PM, Patrick Goold wrote:
>
>> Dear Nav-listers,
>> This is boring compared to recent lunar observations, but I am
>> still trying to determine the position of my front garden using sun
>> sights.  As advised by several of you, I moved past using meridian
>> passage.  On Saturday I took three sights one approximately an hour
>> before LAN, one at LAN and one approximately one hour after.  I
>> then reduced the sights using H.O. 229 (which I discovered is a lot
>> like doing your taxes) and plotted the results on a universal
>> plotting sheet.  The plot showed that the altitude intercepts of
>> the second and third sight intersected at a point very close to my
>> GPS long/lat.  The first one, however, seemed out.  I ran my data
>> through the on-line sight reduction calculator at > www.celnav.de/sightred.htm> and it confirmed the problem.  I cannot
>> find my mistake.  Worksheet attached.  All assistance gratefully
>> received.
>>
>> BTW, the garden is, relatively speaking, stationary.
>>
>> Best regards,
>> Patrick
>>
>>
>> Charles Olson: "Love the World -- and stay inside it."
>>
>> <29 Jan sunsights.pdf>
>
>
>
>
>

   

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