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» Online Classroom   »   » Public Discussion of Cel Nav   » Local noon in CelNavBook

   
Author Topic: Local noon in CelNavBook
Andrewpatrol


 - posted November 16, 2017 03:47 PM      Profile for Andrewpatrol           Edit/Delete Post 
Hi, Bit confused about statement in “Time and time keeping” section on Page 14, #rd Para.
It states that sun bears due south at local noon from northern latitudes always. And Vice versa.
But if the sun has a declination of 23 degrees near the height of summer and I’m at 2 degrees north then wouldn’t the sun bear north?

Confused Andrew

From: Rushworth, Australia
David Burch


 - posted November 16, 2017 04:07 PM      Profile for David Burch           Edit/Delete Post 
I will check the text. Thanks for noting that. If you are between the sun and the equator, the bearing to the sun can be north from north lats.

back shortly.

From: Starpath, Seattle, WA
Capt Steve Miller


 - posted November 16, 2017 04:07 PM      Profile for Capt Steve Miller           Edit/Delete Post 
You are quite correct. In the Northern Hemisphere it depends on your actual latitude as to whether the Sun is North or South of you at the time of Meridian Passage.

The important point is that the Sun is ON YOUR MERIDIAN at Local Apparent Noon. It should be quite apparent to you if the Sun is North or South of you as you observe it.

The same applies in the Southern Hemisphere - your actual Latitude determines whether the SUN is North or South of you at Meridian Passage.

Remember that ALL BODIES have a Time of Meridian Passage. ONLY the SUN has a special Name - being Local Apparent Noon (LAN).

From: Starpath
David Burch


 - posted November 16, 2017 04:20 PM      Profile for David Burch           Edit/Delete Post 
Thanks again for noting that... i must admit to having rounded things off a bit this early in the book, where we have got into the details of special cases.

But your sharp eye and understanding of the principles are correct.

We might note that in these conditions, a noon sight will be very difficult, and indeed when sailing under the sun to get from north of it to south of it is precisely where mariners learn that they are happy they know how to do star sights. The sun will be too high for good sights during mid day and the bearing will be roughly due east all morning and due west all afternoon so running fixes are not practical either.

on the other hand there are exceptions, as you note, namely just a few degrees above the equator and the sun at 23.45N and you can do sights and the sun is north.

From: Starpath, Seattle, WA


All times are Pacific  
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