NavList:

From: John H <apacherunner@gmail.com>
Subject: [NavList] Re: Sunrise - the Positive Side
To: garylapook@pacbell.net
Date: Monday, May 6, 2013, 2:13 PM

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Thanks for Falconer's poem.   That's wonderful!     I really enjoy doing sunrise and sunset observations - it makes me feel connected to history, and I also like to think about all the oddities of refraction. 

I'll stay away from the Earhart stuff, but here's cute trick: if you're at a beach or very close to sea level near sunset - lie down on the ground.  When you see the upper limb just vanish, jump up, and you'll regain the upper limb for a few seconds due to dip angle changes.   I suppose you could try to calculate the radius of the earth using this, but my attempts only got me to within factors of 3-5 or so, but that's refraction for ya. 

On Mon, May 6, 2013 at 10:03 AM, Don Seltzer <timoneer---com> wrote:

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Jeremy C wrote: I tend to agree with Byron. It's easiest to observe and compute the amplitude on the celestial horizon.

In my standing orders, I have it stated that azimuths and amplitudes are to be shot every watch when the opportunity presents itself.

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I think it worthwhile to repost William Falconer's 18th century description of the routine:

'The dim horizon lowering vapours shroud,
And blot the sun yet struggling in the cloud;
Thro' the wide atmosphere condensed with haze,
His glaring orb emits a sanguine blaze.
The pilots now their azimuth attend,
On which all courses, duly form'd, depend:
The compass placed to catch the rising ray,
The quadrant's shadows studious they survey;
Along the arch the gradual index slides,
While Phoebus down the vertic-circle glides;
Now seen on ocean's utmost verge to swim,
He sweeps it vibrant with his nether limb.
Thus height, and polar distance are obtain'd,
Then latitude, and declination, gain'd;
In chiliads next the analogy is sought,
And on sinical triangle wrought:
By this magnetic variance is explored,
Just angles known, and polar truth restored.'

from The Shipwreck

Don Seltzer

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