I got it working. I now realize that the final line is the array that is the position expression. Everything else is just inconsequentially named variables used to populate the final array.
What if I wanted to display the position of the object on screen? Is there a way to link some text on the screen to one of those variables in the position expression?
Precisely, I want to display the distance of the moon from the planet it is orbiting, as well as the time (taking the values and multiplying them by whatever value is necessary to get them from pixels to astronomical units)