# NavList:

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

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Re: "A Star To Steer Her BY"????
From: FS
Date: 2005 Jan 31, 21:00 -0800

```--- Joe Shields  wrote:
> Chapter 2 has several diagrams
> that are most
> upsetting.  They show a FLAT earth with a celestial
> object so close to the
> earth surface as to suggest the difference in
> measured angle with the
> horizon (Ho) is due to the fact that the object's
> rays are approaching at a
> different angle instead of the object's parallel
> rays hitting different
> spots on the earth at different angles due to curved

Joe-

I don't have a newer version, but I do have this book
and I would defend that diagram, a variation of the
"very tall flagpole" analogy, as being quite useful
for gently easing beginners into the concept of
circles of equal altitude.  I am currently teaching a
beginner-level celnav class and that is in fact the
first diagram I draw to start explaining the
underlying principle.  Then I explain how the diagram
is flawed and present the "parallel light
rays/corresponding angles" diagram as being much
closer to the truth, but even it is still flawed by
ignoring parallax, (which is in play for all Solar
System bodies, not just the moon)

I also have a large library and similar diagrams are
in many similar books, including Hobbs, Wright,
Cunliffe, Toghill, Turner, and (I think) the newer
Schlereth.  Others do indeed avoid this diagram.

Diagrams help authors to get points across, like the
huge exaggerations in the typical diagrams
illustrating elliptical orbits, dip of the horizon,
and refraction.  It isn't necessary to be upset by too
literal an interpretation.

Hey Celestaire, I vote please don't phase out this
book!  It is a fine beginner's text!  If there's one
to get rid of, it's the new one by Meyrier!  Pretty
color diagrams, but I found it useless.

-Jeff

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```
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