`  == needs work ==  A very wordy article for a simple concept. Mean longitude is just the angular distance from a reference direction which a body would have if it moved at a uniform angular rate, rather than the non-uniform rate which occurs because of an elliptical orbit. That's it. The second paragraph is discussing, in a convoluted, repetitive fashion, so-called mean elements, which have nothing to do with mean longitude. Mean elements are a sort of average over a long time period. Yes, you can have a mean longitude as part of a set of mean elements, but this ``mean mean longitude`` thing is a little contrived. I had to search for it to find out what it was supposed to be, and only came up with a couple of hits.   `