The planets, I learned when I was 11, “dance and weave behind the sun”.

I still remember that phrase because it made an enormous impression on me. It was magical. Musical. Mythical. And, of course, made up. But I didn’t know that until years later.

In that moment I pictured an immense and fiery Pied Piper playing a thermonuclear recorder, leading a string of little planets on a merry jig through the cosmos. It’s such a fantastic image that it remains with me today, lingering as a small doubt about the veracity of the science I learned later. When I see Mercury or Mars on a dark midnight, a pagan, feral part of me wonders if the other planets are lined up behind them, ready to start the night’s wild rumpus.

This weekend a less dramatic but much more real procession took place in cities around the world. The “March…