Celestia Forums

I've been looking at various bodies' Perihelion and Aphelion lately using the Ecliptic Grid and while focusing on Eris came across some details that don't match. The Perihelion of Eris in Celestia is roughly 194.5° and yet all the data I can find online says it should be 187.3°. Am I looking at the details wrong or is there something else at work? The Ascending Node appears to be in the right place (35.9°), just not the Perihelion.

P.S. I only focused on Eris because it was the last on my list.

From the definition in outersys.ssc:

That makes the longitude of the pericentre 187.186 in Celestia, just a tenth of a degree away from the figure you quote. I'm not sure why you should be finding such a difference experimentally, but I'd guess it's something to do with the fact that longitude of the pericentre is a very peculiar angle: measured along the ecliptic as far as the node, and then along the orbit as far as the pericentre.

Grant