Of course, Jupiter didn’t leave the Solar System, become invisible, or any such thing. But, we haven’t seen it for a while in the evening skies. And, observers who have stayed up late or got up before dawn have been seeing Jupiter. It just hasn’t been visible at sunset in quite a few months.

Since ancient times, people have looked at the sky and observed that some “stars” appeared to wander from constellation to constellation. These wandering “stars” were called planets. ...