Planets is, as Cool Infographics describes it, “an interactive solar system visualizer.” 

It’s described as “a great way to understand retrograde motion.”  I don’t have a clue what that is, and I’m not sure how accessible it is to English Language Learners (though I think, perhaps, that someone more versed in science might be able to use it with ELL’s). 

But it sure looks cool.

I’ll place the link on my Science page.