<p>The major axes of the planets are not aligned.</p>

<p>The major axis passes through the perihelion, the solar system barycentre and the aphelion. So by <a href="http://ssd.jpl.nasa.gov/txt/p_elem_t1.txt" rel="nofollow">looking up</a> the <a href="https://en.wikipedia.org/wiki/Longitude_of_the_periapsis" rel="nofollow">Longitude of perihelion</a> we can find the direction of the major axis:</p>

<pre><code>planet  Longitude of perihelion 
M       77
V       132
E       103
M       -24
J       15
S       93
U       171
N       45
</code></pre>

<p>There is no evidence of alignment.</p>

CC BY-SA 3.0
2015-11-28T16:12:41.217Z
2015-11-28T16:12:41.217Z
James K
<p>The current longitudes of perihelion show no alignment. Furthermore, they change because all the planets have <a href="http://farside.ph.utexas.edu/teaching/336k/Newtonhtml/node115.html" rel="nofollow">orbital precession</a> - that is, the longitude of perihelion changes by between 0.36 arcseconds/year for Neptune (i.e. the longitude of perhelion goes through the full range of angles in 10,000 years) to 19.5 arcseconds/year for Saturn. So not only is there no alignment, but the relative directions of the semi-major axes change comparatively quickly.</p>

CC BY-SA 3.0
2015-11-28T17:15:13.083Z
2015-11-28T17:15:13.083Z
ProfRob
<p>So I'd like to ask whether the semi-major axis of planetary orbits are aligned? Logically, they shouldn't be, but many websites act as if they are. If they're not aligned, what's the angle between the reference xy axis and the semi-major axis of the orbits of planets?</p>

<p>Thanks!</p>

<orbit><planet>
Alignment of Semi-Major Axis of Orbits
HLP
# Alignment of Semi-Major Axis of Orbits

(Asked by: username_0 on 2015-11-28)

So I'd like to ask whether the semi-major axis of planetary orbits are aligned? Logically, they shouldn't be, but many websites act as if they are. If they're not aligned, what's the angle between the reference xy axis and the semi-major axis of the orbits of planets?

Thanks!

**Tags:** orbit, planet

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## 2 answers

### Answer by username_1 on 2015-11-28. Score: 3

The major axes of the planets are not aligned.
The major axis passes through the perihelion, the solar system barycentre and the aphelion. So by looking up the Longitude of perihelion we can find the direction of the major axis:
planet  Longitude of perihelion 
M       77
V       132
E       103
M       -24
J       15
S       93
U       171
N       45

There is no evidence of alignment.


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### Answer by username_2 on 2015-11-28. Score: 3

The current longitudes of perihelion show no alignment. Furthermore, they change because all the planets have [orbital precession](http://farside.ph.utexas.edu/teaching/336k/Newtonhtml/node115.html) - that is, the longitude of perihelion changes by between 0.36 arcseconds/year for Neptune (i.e. the longitude of perhelion goes through the full range of angles in 10,000 years) to 19.5 arcseconds/year for Saturn. So not only is there no alignment, but the relative directions of the semi-major axes change comparatively quickly.


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