Back in the good old days of 1.x, you could draw a line, then draw an object, and make the object move along whatever line that was. It was great.
Then the lovely redesign of Impress came, and that user-defined motion path feature got lost along the way. It was a sad time.
However, now in 2.3 it's back! It works slightly differently, but it's great. In addition, you can edit the existing motion paths like the stars, etc. Here's how it works.