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From: Peter Fogg (no email)
Date: Wed Feb 04 2004 - 00:18:29 EST
Renee Mattie wrote
> I also have (for
> Long 153d 54.8' W
> LAT 038d 46.1' N
> 2002 Sep 9 22:12:34 UT)
>
> GHA 153d 50.'
> DEC 005d 06.8'
> Hc 055d 20.7'
> Azimuth 179.9d
> >From the National Observatory website.
> Which gives me
> Intercept 22.8 nm AWAY
>
> The big difference here is DEC
Renee, there seem to be 2 inconsistancies, the DR latitude which you stated
earlier as
>5) arrive at DR #2 39d46.1'N 153d54.8'W, at 22:12:34 UT,
and the date, 39 hours after the 9 Sep DR. The declination is accurate for
the 9 Sep.
> I do not have another reference for GHA & DEC
> for 2002, so I put my faith in the national observatory.
> Where did you get your data? Which do you trust?
and
> I've seen several good suggestions in the DIY plotting charts
> thread that sprang up from my questions. Do you have more?
One answer to both:
I use a book called 'The Complete On-Board Celestial Navigator'
It has 5 years of almanac data and not only blank plotting sheets but worked
out examples showing how to reduce a sight and plot it,
and much else besides.
Celestaire may stock it http://www.celestaire.com/
or you can find it at Amazon, this link is fairly long
http://www.amazon.com/exec/obidos/tg/detail/-/0071396578/qid=1075868757/sr=1-1/ref=sr_1_1/002-9746912-6430441?v=glance&s=books#product-details
but leads to more information, reviews, etc.
Just by the way,
> For part 5 of Leg 88, we are within a 10th of a minute.
> Hs 054d 48.1'
> IC -000d 02.5'
> Dip -000d -3.0'
> Ha 054d 42.6'
> Ac 000d 15.3'
> Ho 054d 57.9'
One value, the altitude correction, is more accurate than my approximation,
but your dip correction is the other way around.
For dip one solution is to use a simple table, where -3' applies to all
heights of eye between 6 and 13 feet.
Another is the formula: square root of height of eye x .97 (for feet) or
1.76 (for metres)
So here with height eye of 9 feet: 3 x .97 = 2.91
> You said that you wanted to check your results against the "official"
> answers. As far as I can tell, they have not been published.
> Dan Hogan has stated that he currently has higher priorities.
Well, that's sad news. Perhaps they'll turn up in the fullness of time.
We live in hope.
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