# What is the orientation of planetary orbits?

I'm working on a planetary motion simulator. I've been working through the equations anomaly, eccentricity, etc. The one thing I'm curious about is if all the ellipses are oriented the exact same way (the direction of the periapsis of all planets are pointing the same way), or is it different for each planet?

What would this be called? I've only seen eccentricity and inclination.

## 1 Answer

No, the planet orbits do not have their major axis aligned.

http://en.wikipedia.org/wiki/Orbital_elements

You have Inclination and Longitude of the ascending node defining the plane, and Argument of periapsis defining the ellipse orientation in that plane.

• Where is the reference for your answer? Mar 7 '14 at 6:50
• Which kind of reference do you want? Mar 7 '14 at 12:01
• A scientific one? Everyone is good to say: No, the planet orbits do not have their major axis aligned. But astronomy is based upon observations. So where is the study that shows that? Mar 8 '14 at 4:26
• Orbital elements "Inclination", "Longitude of the ascending node" and "Argument of periapsis" would not be necessary if the planets orbits were coplanar and alligned, isn't it? Planets would always be over the ecliptic in sky if their orbits were coplanar, isn't it? There would be no precession of the perihelion of Mercury as predicted by General Relativity if major axis were aligned, isn't it? Just go out of the shell and see. Mar 10 '14 at 14:39
• I'd say Envite's explanation of terms and link to Wikipedia's orbital elements page is sufficient. Then a planet's "ascending node" and "argument of perihelion" could be found on a planet's Wikipedia page. For example Mars ascending node is 49.562º and argument of perihelion is 286.54º. See the right side of en.wikipedia.org/wiki/Mars under the heading Orbital Characteristics Apr 2 '14 at 4:03