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Re: Silicon Sea Leg 88 questions
From: Peter Fogg
Date: 2004 Feb 4, 16:18 +1100
From: Peter Fogg
Date: 2004 Feb 4, 16:18 +1100
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.