PDA

View Full Version : Sol's pole star(s)?



Matthias
2009-Jan-30, 08:03 AM
This is a two-part question, I suppose.

a. Does the sun have any good pole stars? By 'good', I mean star magnitudes below +15 or so, or stars appearing in Celestia's database.

b. What are the closest classically-named stars that would align best with the sun's north and south poles?

I'm guessing these stars would be determinable once you knew what the angle of the sun's rotational axis would be relative to the earth's at a given time of year? Earth's angle of procession (?) is more or less constant (so Polaris and Sigma Octantis [looking up Wikipedia] are constant for the Earth) but from the Earth's perspective the Sun's axis appears to process in a 1-year cycle (I'm guessing) so we have take the time of year into account...

grant hutchison
2009-Jan-30, 12:01 PM
The Sun's rotation axis is in a more-or-less fixed orientation. I imagine it may precess very gently under the gravitational influence of the planets, but the IAU/USGS pole definition (http://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html) contains no precession terms, indicating that the effect is small and/or slow.
From my link, you'll see that the Sun's north pole lies at RA 19h04m31s, Dec 63.87N. That puts the south pole at RA 07h04m31s, Dec 63.87S. You can check a star atlas for stars near these positions.

Grant Hutchison

Matthias
2009-Jan-31, 10:36 AM
Okay..... given the values above I did some research (well I wouldn't really call it research, I was just messing around with Cartes du Ciel and Celestia and www.alcyone.de.)

Anyway, going by the coordinates Mr. Hutchison very helpfully posted (thank you sir), the nearest "named" star for the solar north pole star is Pi Draconis (58 Dra) -- though 55 Draconis (and a host of 'anonymous' stars) are closer to the RA/dec coordinates -- if you count Bayer designations as names. Otherwise the named star closest to the sun's northern pole would be Aldib/Altais/Nodus Secundus (Delta Draconis).

For the solar south polar star, it's either Alpha Pictoris or maybe Delta Volantis (judging purely visually using Celestia.

Interestingly, wikipedia.com (or Starry Night Pro which it cites) says that Alpha Pictoris and Omicron Draconis are Mercury's pole stars, and Mercury and its orbit have are not tilted at a great angle relative to the Sun's equator. However Cartes du Ciel places Omicron Draconis further away than 58 Dra and even 55 Dra from the coordinates for the sun's north pole, so *shrug*