NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: How far is polaris?
From: Frank Reed
Date: 2007 Nov 22, 05:49 -0500
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 --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---