File talk:Eris Orbit.svg

Hello, there appears to be a problem with Eris's orbit in the left hand diagram in the image. The Sun should be at one focus of the ellipse and it clearly isn't. The perihelion (the position of the closest point in the orbit to the Sun) should be at the opposite end of the orbit from the aphelion (the farthest point in the orbit), not off to one side. Look where Eris's orbit intersects Neptune's fairly circular orbit. In reality, with a perihelion of 38 AU, Eris never intersects Neptune's orbit at 30 AU. Hopefully this won't be hard to fix. WolfmanSF (talk) 08:10, 5 January 2014 (UTC)

Hello Wolfman. The orbit of Eris is very eccentric and has a very steep inclination of 44 degrees. The diagram is a near polar view of the ecliptic, so you're looking (almost) straight at the planet's orbits, but seeing Eris' orbit at a diagonal angle. So Eris never intersects Neptune's (or Pluto's) orbit. As for the Sun not being at the focus of the ellipse, it has to do again with the viewing angle. You'll only see it in the focus when the viewing angle is perpendicular to at least one of the axes, which is not the case here.

The reason I included three different views from different angles was these orbital properties, while one polar view of the ecliptic would suffice for a planet's orbit. You'll get a better idea of the orbit if you follow the link in the description (here it is, you need to have Java installed to work) which contains a 3d applet of the orbit that you can move and rotate, which was the source I relied upon to make this diagram. Cheers! -- Orionist ★ talk 22:47, 7 January 2014 (UTC)

From my perspective, the problem arises not only because Eris has an inclined orbit, but because the vantage point used by the applet is too close. If it were sufficiently far away, the orbit wouldn't appear to intersect Neptune's from viewing angle perpendicular to the ecliptic. WolfmanSF (talk) 04:06, 10 January 2014 (UTC)

The applet can zoom out to a very far vantage point and the view stays the same. My guess is that the applet never reaches a perpendicular angle to the ecliptic (that's why I said above it's a "near polar view"), as the view of both Eris' and Pluto's orbits changes when you rotate the diagram in the applet, which produces the intersection with Neptune at specific angles. The angle I chose when making this diagram was the one similar to other diagrams I found in online sources (here is another one from NASA). I tried looking for other orbit simulators (just tried again and this is the best I could find) but I don't know how accurate they are. If you know of a source with a more accurate polar view, please post a link to it. Cheers! -- Orionist ★ talk 21:14, 12 January 2014 (UTC)