NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: How far is polaris?
From: Fred Hebard
Date: 2007 Nov 22, 12:10 -0500
From: Fred Hebard
Date: 2007 Nov 22, 12:10 -0500
Frank, If you could expand on the speed of light business, that would be great. Fred On Nov 22, 2007, at 5:49 AM, frankreed@HistoricalAtlas.net wrote: > > 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 -~----------~----~----~----~------~----~------~--~---