<p>Sirius is a binary system, composed of a main sequence star (Sirius A) and a white dwarf (Sirius B). The two orbit each other with a period of about 50 years, and the eccentricity given on Wikipedia is the eccentricity of the stars' orbits around one another. The inclination, according to <a href="http://adsabs.harvard.edu/abs/2017ApJ...840...70B" rel="nofollow noreferrer">Bond et al. 2017</a> - the paper Wikipedia references for both numbers - is described as the inclination of the "relative visual orbit", leading me to believe that the inclination is defined based on a plane relative to the point of view of an observer on Earth.</p>

<p>Something it's important to realize is that <a href="https://physics.stackexchange.com/a/148670/56299">stars don't follow Keplerian orbits</a>, because of the non-point-like distribution of matter in the galaxy; the motion of a star around a galaxy is therefore somewhat more complicated than the motion of a star in a binary system.</p>

CC BY-SA 4.0
2018-08-19T15:24:04.630Z
2018-08-20T00:33:32.040Z
2018-08-20T00:33:32.040Z
HDE 226868
<p>I understand Planetary Eccentricity and Inclination.  However when it applies to a star, does the centre or ecliptic plane refer to the Sun or the Galactic Centre?</p>

<p>The star Sirius for example, 136.336 ± 0.040° inclination, the angle at which it is inclined to Sun, Earth or Galactic Centre?</p>

<p>The star Sirius has an Eccentricity of  0.59142 ± 0.00037.  The only thing the star orbits is the Galactic Centre (Sagittarius A*) so I guess that is the centre?</p>

<star><inclination><eccentricity>
Eccentricity and Inclination of a Star
MiscellaneousUser
# Eccentricity and Inclination of a Star

(Asked by: username_0 on 2018-08-19)

I understand Planetary Eccentricity and Inclination. However when it applies to a star, does the centre or ecliptic plane refer to the Sun or the Galactic Centre?

The star Sirius for example, 136.336 ± 0.040° inclination, the angle at which it is inclined to Sun, Earth or Galactic Centre?

The star Sirius has an Eccentricity of 0.59142 ± 0.00037. The only thing the star orbits is the Galactic Centre (Sagittarius A\*) so I guess that is the centre?

**Tags:** star, inclination, eccentricity


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## 1 answers

### Answer by username_1 on 2018-08-19. Score: 5 | Accepted answer

Sirius is a binary system, composed of a main sequence star (Sirius A) and a white dwarf (Sirius B). The two orbit each other with a period of about 50 years, and the eccentricity given on Wikipedia is the eccentricity of the stars' orbits around one another. The inclination, according to [Bond et al. 2017](http://adsabs.harvard.edu/abs/2017ApJ...840...70B) - the paper Wikipedia references for both numbers - is described as the inclination of the "relative visual orbit", leading me to believe that the inclination is defined based on a plane relative to the point of view of an observer on Earth.

Something it's important to realize is that [stars don't follow Keplerian orbits](https://physics.stackexchange.com/a/148670/56299), because of the non-point-like distribution of matter in the galaxy; the motion of a star around a galaxy is therefore somewhat more complicated than the motion of a star in a binary system.


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