# NavList:

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

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Re: Longitude via lunar altitudes, simplified
From: Peter Fogg
Date: 2007 Feb 15, 15:05 +1100

Dan Walden wrote:

Many of the astronomy and navigation
texts from the 1800's ... have references to longitude by lunar altitudes.  Since this
was before LOP, most discuss only longitude assuming latitude by one
of a number of other methods  ...

Position lines (LOPs) are not a necessary part of the process of determining time/longitude via lunar altitudes.

Watch Correction (WC) and Longitude can be obtained simply by using Calculated and Observed Altitudes (Hc and Ho) as follows:

Moon(UL) etc

Watch Time        WC           Longitude             Hc                  Ho            Intercept

1.    9h 07m 55s               0        W15d 22.5m    37d 38.9m     37d  36.5m       A2.4m

2.    9h 07m 55s     Slow 20m    W20d 22.5m    37d 47.2m     37d  36.5m      A10.7.4m

Let G  =   Hc1  Ho  =  2.4

Hc2  Hc1     8.3

Watch Correction

G x 20m = 5m 47s  Fast

Longitude

W15d 22.5m  G x 5d  = W13d 56m

The results are identical to those given earlier.

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