# NavList:

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

**Re: How far is polaris?**

**From:**Mike L

**Date:**2007 Nov 26, 04:25 -0800

> 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. > According to WIkipedia polaris is at "2400 Astronomical units". An astronomical unit is roughly the distance from the earth to the sun. Now even a schoolboy (at least in my day) could work out that as the earth moves from one side of its orbit to the other it moves two astronomical distances so the angle of wobble is tan-1 (2/2400) which I make 2.8' The limited bit of the table I have indicates a difference of around 1' at certain times of the year, which does seem to correspond roughly to the expected wobble of 2.8' However, wikipedia gives the Parallax (�) is given as 7.56 � 0.48 mas (minutes of arc), so clearly I can't be like some and assert I fully understand the subject. Mike --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To unsubscribe, send email to NavList-unsubscribe@fer3.com -~----------~----~----~----~------~----~------~--~---