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Re: Celestial: 19th Century Methods
From: Hanno Ix
Date: 2014 Nov 25, 21:09 -0800

Frank,

here is a question concerning astro-dynamics.

I think the problem is actually one of relativity, and I know you are an

expert on that topic. Perhaps, though, it can be treated approximately

with classical dynamics, however I would not know how. I am posing it

here in colloquial terms.

I am considering a 2-body planetary system with one body's mass exceeding the other's by orders of magnitude. The initial conditions were such that the smaller body

orbits the bigger one in an orbit quite different from a circle. The initial distance

is, say, 10 light minutes. So, at any instance, one body "sees" the other at a location were it was some time ago - so, initially 10 minutes ago. This, of course, is different

from the classical assumption that gravitational interactions are instantaneous.

Question: How does this different assumption change the orbit calculations and

the predicted orbit? The observer's point of view of this system is assumed "far away" but on a straight line going through the bigger body and perpendicular to the plane of motion - if there is one.

You are a busy man, so therefore I will ask you only: Do you know of literature that treats this and related problems in a semi-classical way? Do, you think, it can be treated this way - at least in approximation? In all the dynamics books I have no such

problems of retarded interaction is described.

Thank you so much, and best regards

On Tue, Oct 21, 2014 at 9:46 AM, Frank Reed <NoReply_FrankReed@navlist.net> wrote:

CELESTIAL NAVIGATION: 19TH CENTURY METHODS
Coming up Saturday and Sunday November 1 and 2 at Mystic Seaport in Mystic, Connecticut, I'm running my class in celestial navigation as it was practiced in the 'Age of Sail'. We'll focus on actual observations made aboard the whaleship Charles W. Morgan on its multi-year voyages to the Pacific to hunt whales in the 19th century. Participants will learn all about sextants, Noon Sun sights for latitude, and traditional time sights for longitude. We'll work with modernized versions of traditional log tables to do the calculations, but we'll also see how to do the work by calculator. All of this is practical, or at least "practicable" in the 21st century, too, and we'll also emphasize how to use these methods to cross an ocean today.
Details here: http://www.reednavigation.com/c19-class/
The photo, taken July 11, 2014 a few miles north of Cape Cod, is from the "38th Voyage" of the Charles W. Morgan. On this voyage leg I was navigating by sextant while everyone else was busy watching those pesky whales. Silly whale tourists: "Oh look, a giant marine mammal swimming majestically alongside our restored whaleship... again!" As if that's more interesting than spherical trigonometry calculations performed with logarithm tables. Sheesh. ;)
Two weeks after this class, we're offering our "lunars" class again. This "19th century methods" class is an excellent introduction for the lunars class if you're considering joining in on that (lunars class details). I'll post a more specific description of that soon.
-FER

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