# NavList:

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

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Re: MP Venus PV Moon Fix Without Plot
From: Greg Rudzinski
Date: 2015 Nov 30, 21:34 -0800

Frances,

Questions:

1. Has this technique got a name? I don't know. It is a special case of time sight for the moment when a body has an azimuth of 90° or 270°.

2. What is Hp ? Hp is a precalculated Hs for a future time. It requires applying corrections to a future Hc with signs reversed. This is how Most aviation CN is done so that azimuths and intercepts can be plotted immediately.

3. Why calculate LHA from Az ? Since the sin of 90° azimuth is 1 then the azimuth formula simplifies for deriving LHA. LHA is summed with GHA to get Longitude just as a time sight for the UT moment of the the prime vertical observation that has been precalculated. The UT is marked when the body touches the horizon on the preset sextant. Enter the Nautical Almanac with UT to get GHA.

4. Where did you get Az ? Az is a given 90° or 270° for a body that is due east or west.

5. How accurate was the resultant fix ? The fix was 2 NM from my actual location at the sea shore. Nothing to brag about :( The horizon wasn't that good is my excuse ;-)

Greg Rudzinski

From: Francis Upchurch
Date: 2015 Nov 30, 20:10 -0800

Greg,

That is fascinating. Must try that.(our Cornish weather no good at moment, can't see sun , never mind venus). Has this technique got a name?

Sorry to be very slow, but would you mind explaining the rationale and details of your method here step by step for dullards like me?

What exactly is Hp pr-set? why use it?

Why calculate LHA from Az? where did you get Az? (compass bearing or what?)How accurate was the resulting fix?

Look forward to your reply and some good weather here for a trial.

Best

Francis

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