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

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Re: How far is polaris?
From: Frank Reed
Date: 2007 Nov 22, 05:49 -0500

```Mike (Isonomia) wrote:
"In other words, A2 accounts for the finite distance of the star! That is to
say, the star wobbles with respect to the background galaxies (can't say
stars because they are too near!!!)

It is absolutely mind boggling to think that a handheld instrument like a
sextant could possibly be affected by the distance to the stars.

It completely turns history on its head. ..."

Aw, sheesh, Mike. Don't go turning history on its head before you've
understood the basics. :-)  No, A2 is not connected with the distance to
Polaris --more than one post has tried to explain this to you further. Let's
work the numbers... The nearest stars are on the order of ten lightyears
away (of the bright navigational stars, there are two closer). How does ten
lightyears compare with the distance to the Sun? Well, that's easy enough if
you remember that the distance to the Sun is very close to eight
lightminutes. Compare eight minutes with ten years... Now, the parallax of
the Sun is a minor, though not necessarily negligible, correction in
celestial navigation amounting to only 9 seconds of arc. The parallax of the
stars, even the nearest, is less important by the ratio of eight minutes to
ten years. I'll let you work the math. Clearly, it's a completely trivial
factor for celestial navigation with a handheld sextant.

But there is an extraordinary effect that you can detect with a handheld
sextant, if you're a careful observer, that might surprise you. It's the
speed of light. Aberration of star light --directly due to the finite speed
of light-- can be detected by observing, very, very carefully, the angular
distances between stars over the course of a year. Your Ebbco isn't up to
the task, but a well-adjusted metal sextant is. And isn't that a bit
amazing: you can measure the speed of light (to one significant digit) using
a handheld instrument.

-FER

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