# Is our solar system 2D?

#### lewdtenant

Ok, this may be a silly question and I probably should have asked it a long time ago..

Do the planets in our solar system rotate around the sun in two dimensions? By that I mean if you take the standard XYZ coordinate system, the planets exist only in the XY plane, right? Or is this just what I'm led to believe by every single picture/animation of the solar system that I've ever seen.

Because if this is true, I find it odd.

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#### Quisquis

It's mostly true. There is some slight variation in inclination relative to the earth, but not much. It appears that this is not necessarily true outside of our solar system though since many extra-solar planets we've seen appear to have a very high inclination.

Check wikipedia for "inclination" and "orbital plane".

#### D H

Staff Emeritus
Quisquis, that is not quite what lewdenant asked. lewdenant asked about whether the planets' orbits lie in the same plane (the key phrase being "rotate about the sun"). Quisquis, your answer was about the rotation of the earth about its axis versus the revolution of the earth about the Sun.

So, first some terminology to straighten things out. Days and years both result from some kind of repetitive motion. What causes days and years are quite different things, so it is best to use different terms. Rotation refers to quasi-circular motion of a body about some axis internal to that body. The Earth rotates about its axis once per day. Revolution refers to quasi-circular motion of a body about some point external to that body. The Earth revolves around the Sun once per year.

The planets do indeed have more-or-less the same orbital plane. Google "ecliptic". This is no coincidence. It is a result of conservation of angular momentum and what happened long ago when the solar system formed. The same thing can happen in galaxies. This is why the Milky Way is more-or-less flat.

#### lewdtenant

Sorry about the terminology. I did indeed mean to say revolve and not rotate. Thanks for the responses.

#### Quisquis

Quisquis, that is not quite what lewdenant asked. lewdenant asked about whether the planets' orbits lie in the same plane (the key phrase being "rotate about the sun"). Quisquis, your answer was about the rotation of the earth about its axis versus the revolution of the earth about the Sun.
I'm pretty sure I answered the question that he meant to ask. The inclination of the other planet's orbital planes relative to earth's orbital plane is very minor was essentially my answer.

I suppose when I said relative to earth, I should have said relative to earth's orbital plane, but that's the only place where I see there being any confusion.

#### D H

Staff Emeritus
Inclination refers to the angle between a planet's rotation axis and the planet's orbital axis. He/she did not ask about planet rotation, period. (Bad pun, sorry.) He clarified his intent before your response:
Sorry about the terminology. I did indeed mean to say revolve and not rotate. Thanks for the responses.

#### Quisquis

From the article on Inclination in wikipedia:

In the solar system, the inclination (i in figure 1, below) of the orbit of a planet is defined as the angle between the plane of the orbit of the planet and the ecliptic —which is the plane containing Earth's orbital path.
That makes it seem that if you are referring to the inclination of bodies in the solar system other than earth, then you are referring to their orbital plane in relation to the ecliptic.

Your definition of inclination seems to fall under "other meanings"

For planets and other rotating celestial bodies, the angle of the axis of rotation with respect to the normal to plane of the orbit is sometimes also called inclination, but is better referred to as the axial tilt or obliquity.

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#### ray b

is most of the little stuff also in the same plain ?
inc the far out clouds of comets ?

#### Quisquis

is most of the little stuff also in the same plain ?
inc the far out clouds of comets ?
Inside of Neptune, everything is in essentially the same plane. Starting with the Kuiper Belt, things move off the plane a good deal more. If you go as far out as the Oort Cloud(where most comets come from), I'm pretty sure that people believe that the material is actually fully surrounding the sun.

http://math.ucr.edu/home/baez/kuiper_oort.jpg" [Broken] is a good image of what the full solar system seems to look like. It's got the orbits of a couple of Kuiper Belt objects in the inset, and you can see how inclined they are. In the main picture you can get a good idea of how huge the Oort Cloud is and how fully it appears to surround our sun.

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#### Lanka

The plane upon which each planet rotates around the sun is roughly the same for all of the planets in our solar system. This is why it is possible to get an eclipse from the planets. Though the planets as well as the asteroid belt all rotate around roughly the same plane, other celestial objects don't have to. For instance, the rotation of the moon around Earth is on a very different plane than the orbit of Earth around the sun. If they were on the same plane, we would have a solar and a lunar eclipse every month. This is true for many other moons in our solar system. Also, comets are not confined to the typical planetary plane. Also, the main planes on which other solar systems rotate is also very different from ours and the same is true for galaxies.

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