NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2016 Apr 11, 10:20 -0400
Phillip
There are two statements in the article which would explain the "insignificance for practical purposes".
The first is when the drift is expressed as less than the Chandler wobble.
The Chandler wobble is a small deviation in the Earth's axis of rotation. It amounts to change of about 9 metres (30 ft) in the point at which the axis intersects the Earth's surface.
Celestial navigation doesn't register a 9 meter displacement.
The second is much clearer: "The variability in TWS excitation signal fully explains the ~20-mas amplitude of the observed change in χ2(t) during the study period."
20-mas is 0.020 arc seconds. In celestial navigation, we generally limit ourselves to 0.1 minutes or 6.0 seconds. Therefore, the drift explained in the article is 300 times smaller then our practical value.
Yes, there is drift in the position of the pole. The magnitude of the drift is too small for us to notice in celestial navigation.
Brad
Actually Frank, I was only half kidding. Currently we use the tables to account for the changes in relative position of the pole star. I realize that the variable in the earths wobble would be a very small one for practical purposes, so that was the joke.
However, the science behind the article appears, to this unlearned eye, to be well documented. so perhaps you might find this a "useful account". http://advances.sciencemag.org/content/2/4/e1501693.full
If the article is hog wash i would appreciate any comments that might enlighten me so that i might not be so easily fooled in the future.
Philip
On 04/09/2016 09:23 PM, Frank Reed wrote:
Sometimes we have to worry that humor doesn't work here. So before anyone goes ballistic on this one, please bear in mind that Philip Lange is surely kidding about changing the Polaris correction tables. :)
By the way, the general media coverage on this particular story is "Internet viral" nonsense --just incredibly poor. Good luck finding any useful account of it.
Frank Reed
