“Anyway,” Bull continued, ignoring Hobble’s remark, “the two really important parts of an orbit are the apoapsis and periapsis.” Using the chalk to indicate points on the circle, “The apoapsis is the point highest from the planet, and the periapsis is the point closest to the planet.”

“Poppyapsis, berryapsis,” Upper Crust said, dismissing the words with a hoof. “How can you keep track of which is which?”

“I’m glad you asked,” Bull said, stepping away from the chalkboard, his hooves clicking merrily on the tile floor as he chanted:

When you’re flying in an orbit
When into space you’re hurled
You need to know your position
In relation to the world

The point of periapsis
Is when you’re closest to the ground
Opposite your apoapsis
As the world you go around

So you don’t get them confused
Here’s a handy trick I know
So you’ll know your altitude
As around the world you go!

Bull paused, then said in a slower chant:
Api is uppy
And peri is not.
Api is uppy
And peri is not.