Gravity and inertia both think they control the universe. In fact, neither gets its own way.
As planets orbit, they are thrown by solar gravitation
Into ellipses, ’gainst their own inertial inclination.
Inertia is a tad annoyed, she’s feeling put upon,
Her whinging echoes through the void – she does go on and on!
“I don’t like changes, I resist ‘em; curvatures I shirk.
The orbits of the Solar System are the Devil’s work:
The planets ought to travel straight, it is their natural way!
Ellipses I’d eliminate – Inertia rules, ok?”
But deep in space, another stirred: “That’s what you think,” said he,
He’d listened in to every word. His name was Gravity.
“My influence is everywhere, benignly interactive.
It makes each bright celestial sphere peculiarly attractive.
My pulling power is so great that things need no assistance
To centripetally gravitate; most offer no resistance.
If I had my way, every star in every constellation
Would race together from afar – a mighty conflagration!”
If you’re a planet, neither fate can bear imagination:
You’d either freeze, or gravitate towards annihilation . . .
So better far to steer a way between these mighty forces –
That’s why the planets choose to stay on their elliptic courses.