Author Topic: Star sight lat and long obs  (Read 4566 times)

AvastMH

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Star sight lat and long obs
« on: December 08, 2014, 02:26:41 pm »
I think I found one of these before but can't recall what to do with it...a lat and long by star sight..see last para of this page:
http://oldweather.s3.amazonaws.com/ow3/final/USCS%20Patterson/Book%207/IMG_5575_1.jpg

Thanks for any advice.  :)

Hanibal94

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Re: Star sight lat and long obs
« Reply #1 on: December 08, 2014, 02:32:50 pm »
Since the respective weather page has an Observed lat and long, I would just enter those instead.
Not sure what to do if there were no lats/longs on the weather page - I'll let the mods answer that one.

Janet Jaguar

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Re: Star sight lat and long obs
« Reply #2 on: December 08, 2014, 02:36:02 pm »
It is an Observed Location, and treated as such, even though it is on the comment page.  I would absolutely also make an event of the full comment to give the time, etc, as I think this is the very first time someone found this on an American ship.  Cool.



Hanibal's answer of having the weather page's observed location also is good, but Philip has said more than once that multiple readings on the same day gives them an estimate on their accuracy.
« Last Edit: December 08, 2014, 06:28:30 pm by Janet Jaguar »

AvastMH

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Re: Star sight lat and long obs
« Reply #3 on: December 08, 2014, 03:20:53 pm »
Cheers Hanibal and Janet.  I'll put those in the observed box and do a full event note as well.
 :)

Kevin

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Re: Star sight lat and long obs
« Reply #4 on: December 09, 2014, 01:31:36 am »
Very cool. A morning or evening star sight is the best kind of celestial fix, since there are typically 3 to 7 stars shot within a few moments of each other, with the result being a 'pinwheel' of intersecting LOPs (Lines of Position). Unless you get a 'cocked hat'.

AvastMH

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Re: Star sight lat and long obs
« Reply #5 on: December 09, 2014, 10:59:17 am »
OK Kevin...this is what I jokingly call a 'fingle-fangle-on-the-dingbat' situation...i.e. I'm completely confused. Is there a nice website that I can use to take me step by step through this one please? Gently so, if possible. Ta! ;D

Kevin

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Re: Star sight lat and long obs
« Reply #6 on: December 09, 2014, 08:08:12 pm »
Oh no, this is for mariner wizards only! There is something on http://en.wikipedia.org/wiki/Celestial_navigation. I will look for something better....

AvastMH

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Re: Star sight lat and long obs
« Reply #7 on: December 09, 2014, 10:37:28 pm »
Thanks Kevin...I think I better get a night's sleep before facing this one....but I'll get there...honest... :D

Kevin

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Re: Star sight lat and long obs
« Reply #8 on: December 10, 2014, 04:28:48 pm »
Here is the standard reference for (sextant) sight reduction. The figure shows the 'navigators day's work' on a universal plotting sheet. The 'pinwheel' I referred to earlier appears in the upper right - a plot of the lines of position (LOPs) reduced from sights of the stars Sirius, Arcturus, and Capella at 0620. The evening stars didn't yield such a nice result as the angle between the LOPs of Vega and Fomalhaut are a bit too close.

http://en.wikisource.org/wiki/The_American_Practical_Navigator/Chapter_20

AvastMH

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Re: Star sight lat and long obs
« Reply #9 on: December 10, 2014, 04:44:57 pm »
Oh golly Kevin...THANK YOU....mind boggling!   I'm going to get to the bottom of this though...but it may take time...and quite a few sheets of paper :D

Janet Jaguar

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Re: Star sight lat and long obs
« Reply #10 on: December 10, 2014, 06:16:34 pm »
That is wonderfully complex, and demonstrates conclusively exactly why even the best navigators very rarely plotted position by the stars.  Very good to know they kept in practice in case a storm blew them off course by an unknown amount.  :)

Kevin

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Re: Star sight lat and long obs
« Reply #11 on: December 11, 2014, 12:26:27 am »
Good navigators prefer stars (actually the whole 'days work') - but since the logbooks require a 'noon' position written out it isn't clear that it often contains a morning star fix carried forward on the DR plot.

It looks kind of complicated but I am happy to have had the chance to sail using only celestial, DR and piloting. I really liked going out on deck and seeing a familiar map of stars overhead. And the useful element of doubt is hard to teach in a GPS environment where you (think) you know exactly where you are.

In fact, the closest I came to a serious accident was running down the line on the GPS display toward (I thought) an offshore drilling rig we were carrying a load of fuel, drilling mud & chemicals to -- but I had put in the wrong waypoint and sailed right onto Trinity Shoal. That was a sinking feeling (so to speak).

Janet Jaguar

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Re: Star sight lat and long obs
« Reply #12 on: December 11, 2014, 12:32:24 am »
OUCH!!! ;D

Kevin

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Re: Star sight lat and long obs
« Reply #13 on: December 11, 2014, 12:43:30 am »
Oh well, there was still two feet under the keel when I realized where we were. Also explained why the AB couldn't steer a straight course - bottom suction - had to apologize to him too!

studentforever

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Re: Star sight lat and long obs
« Reply #14 on: December 11, 2014, 05:33:09 am »
Good to know that if a solar flare or malign superpower knocks out the GPS satellites navigators remember how to plot a position using old techniques. Mind you, I think getting a star fix in the sort of 40 foot waves we've been having round here in the last few days must have been a bit difficult!