# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Interpolation to latitude
From: Joe Schultz
Date: 2009 Nov 15, 23:45 -0800

```And back to Inuik's topic.

Thank you Peter!  The nearest complete paper nautical almanac is about 250 Smi
from me.  Thanks for going to the source.  For the novice, Peter's final
quote is how most of us operate - sometimes the assumptions become too
automatic.

Inuik, looks like you understand the longitude correction (but I'm not too
sure who Jerry is - hee hee).  This type of exercise is good for much more
than planning a round of sextant shots.  Let's work one more practical
example.

Exercise: you are planning a day of fishing, in the Gulf of Mexico off
Yankeetown, Florida, and want to return and trailer the boat before dark.
Find: sunset 28JUN2010 at N29d W82d45m.
Almanac data (via USNO website): sunset N30 = 1905.  N20 = 1843.
Answer (in local zone): ZT = 1843 + 20m - 29m = 1834 "S" 28JUN2010 = 0034 "Z" 29JUN2010.
Answer (in GMT/UT): ZT = 1843 + 20m + 5h 31m = 0034 "Z" 29JUN2010 = 1834 "S" 28JUN2010.

Bonus for the North American readers: your helper lives in Yankeetown.  When
(by his watch) does he need to be at the boat ramp with your trailer?
Answer (in local zone): 1834 + 1h + 1h = 2034 "R + DST" or 8:34PM EDT 28JUN2010.
Answer (in GMT/UT): 0034 - 6h + 1h + 1h = 2034 "R + DST" or 8:34PM EDT 28JUN2010.

This is a real place with a real boat ramp.  And, as promised, why is it OK to
apply a linear interpolation for the LAT CORRN?

Derrick, an interpolation is a mathematical process where you find an unknown
value between two other known values.  In and of itself, an interpolation has
no physical meaning.  That's not the answer, by the way - it's a start in the
thinking process.  I see the "mil" in your address - thanks for serving.
Bluejacket, sandcrab, wingnut, or one of the mudsucker flavors?

Joe

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