Talk:Polaris

The figure for the semimajor axis of the companion, given as 5 AU, is obviously in error. Here's why: a = cuberoot of the total mass times the period squared (say, 30 years). For any reasonable value of M (which can hardly be less than 10 times our sun's, given the luminosity of Polaris A), the size of the orbit comes out at about the distance of Pluto from the sun--not Jupiter!--for having extra mass in the system, causes them to revolve FASTER.

Addendum. When i wrote the foregoing, i didn't have precise figures for Polaris's mass. By the Cepheid relation M = .58 + .24 log P (in days) the mass of the primary should be about 5.29 times the Sun (not 8 to 10, which is more typical of a F-type supergiant of this luminosity). Assuming for the moment that the unseen companion is about 300 times dimmer than the visible primary, this comes out to a mass ratio of about Ma/Ma+Mb of 0.75; & the semimajor axis is 18.35 Astronomical Units (or 18.7, if you use Burnham's period of 30.5 years)...more like the distance of Neptune. (Its eccentricity takes the two stars from 7 to 29 AU separation.) The displacement of the primary amounts to about 4.58 AU, or 426 million miles, presumably the source of the quoted figures (with 290 million miles, given by Burnham, the mass of the companion becomes very small indeed). But this is a small portion of the entire orbit.

This is a good subject for calculating derived figures on, for the values derived from Cepheid equations can be tallied with the observed type F3 main sequence third star; thus the range of distances possible is fairly narrow, in comparison with many other supergiant stars, e.g. Canopus or Rigel.

Dominance of the North?

I once read that a major factor contributing to the dominance of the northern hemisphere in such activities as ocean navigation and widespread colonization and travel was due to the fact that there is a North Star, but no South Star. Has anyone else heard this? --Golbez 21:31, Sep 27, 2004 (UTC)

Nope I haven't seen that one, but see also Guns, Germs, and Steel. — RJH 20:01, 17 January 2006 (UTC)

I could figure out the point in the sky thats south based on the constellations in one night of looking up there. Ancient people have figured out things a lot more complicated than that.

Join this article?

This article is of the same subject as North star, and Pole star. i think it would be good to join these articles.

above by 12:54, user:Gxojo at 12:54, 28 Jan 2005

• No, North Star is not about Alpha Ursae Minoris per se. It is about all North Stars, such as will be Vega in the future. And pole star covers both North Star and South Star (or should). Polaris, inappropriately named, covers only Alpha Ursae Minoris. 132.205.15.43 04:00, 1 Feb 2005 (UTC)

Visibility from the Southern Hemisphere

Polaris can be visible from locations near the equator in the southern hemisphere. Polaris is about 0.75° from true north. At an elevation of 3km, horizon dip is 1.75°, and atmospheric refraction can be good for another 0.5°, depending on conditions. Adding these up, Polaris can rise over the horizon at locations as far as 3°S.

At 3km elevation, atmospheric extinction at 3° from the horizon can be as low as 2 magnitudes, and as low as 5 magnitudes at the horizon itself. Under these near perfect circumstances, Polaris could be a naked eye magnitude 4 at (or just south of) the equator, and up to magnitude 7 at 3°S.

Distance from the north pole

Shouldn't it be 42', not 42" ? Or what exactly does " mean (compare the coordinates)? Otoomet 16:45, 2 July 2006 (UTC)

Oops, that's embarrassing. I actually wrongified that part of the article months ago. The HTML should have read ′ instead of ″. I've fixed it. -- Xerxes 20:58, 2 July 2006 (UTC)

Polaris Ab

This 10 Jan 2006 news release contained material an amateur like me would be interested to read in the article:

• "The companion proved to be less than two-tenths of an arcsecond from Polaris — an incredibly tiny angle equivalent to the apparent diameter of a quarter located 19 miles away."
• By watching the companion star in its 30-year orbit, astronomers expect to learn not only the stars' orbits but also their masses, valuable because it is the nearest Cepheid variable, the brightness variations of which are used to measure the distances of galaxies and the expansion rate of the universe.

--Wetman 06:10, 18 October 2006 (UTC)