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Author
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Topic: LAN Example on Page 3-16
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Bill Riner
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posted June 12, 2005 07:31 AM
I have a question about the LAN example on page 3-16. You have a declination of 19 deg 36.0 min on line 3-2. Using the 2005 Almanac, I get 19 deg 29.9 min. I haven't been able to figure this out. Could it be that the example date is 1978 and my Almanac is 2005?
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David Burch
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posted June 12, 2005 03:31 PM
Yes, that seems to be the case. I have checked this with our perpetual almanac as well and sure enough it varies that much.
the main difference is the location within the leap year cycle, 2005 - 1978 = 27 years. Had this been divisible by 4, the difference would not be nearly so large. Here are some data for July 25 at at 20h 50m GMT
1 2005 = N 019° 29.5'
2 2004 = N 019° 26.3'
3 2003 = N 019° 36.2'
4 2002 = N 019° 33.0'
1 2001 = N 019° 29.8'
2 2000 = N 019° 26.6'
3 1999 = N 019° 36.4'
4 1998 = N 019° 33.2' etc...
but there still is some creep away from this cycle due to the "precession of the equinoxes", and in 27 years — seems to be dating our school a bit here — that begins to show up.
From: Starpath, Seattle, WA
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David Burch
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posted June 12, 2005 03:39 PM
Just a last thought. The (implied) idea of using almanac data as about interchangeble every 4 years, only applies to sun and stars. Moon and planet data will not behave this way at all.
There is a note in the almanac text pages somewhere that explains how to make the yearly estimates of these changes for sun and stars.
From: Starpath, Seattle, WA
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Bill Riner
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posted June 16, 2005 10:26 AM
Thanks for that great explaination. I'll use the perpectual almanac instead.
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Bill Riner
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posted June 19, 2005 11:47 PM
Do you have LAN examples available for 2005? I'd like to use the paper Nautical Almanac instead of the perpetual because that's how I'll be doing it on the water.
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David Burch
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posted June 25, 2005 12:01 AM
We missed this note. I apologize.
Yes we can find some of these, but it will take a couple days. In the meantime, you will get very good practice by just changing the year to 2005 and working the ones you have. Just do a couple and then tell us here which ones you did in this manner and we can check to see if you got them right.
In reality, the very fact that we can teach effective cel nav techniques using 1978 data that still works perfectly fine today, is testimony to the beauty of cel nav.
In any event, we will get some 2005 full noon sight curves for you to analyze.
From: Starpath, Seattle, WA
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