In the last lesson, Eon learned that everything in 3D is controlled by numbers — position, scale, and rotation. Animation is the same idea with one magic twist: the numbers change over time.
Spinning the moon
To make a 3D moon spin, you don't redraw it. You take its rotation on the Z axis and slowly increase the number — a little more each frame — and the moon turns all by itself.
What a keyframe does
You don't set every single frame by hand (there can be thousands!). Instead you set a few keyframes — like "at second 0 the rotation is 0°" and "at second 4 the rotation is 360°" — and the computer fills in everything in between. That filling-in is called interpolation.
Keyframes are the corners of the motion. The computer connects the dots into smooth movement.
A bonus from real space
While spinning the moon, a great question popped up: does the real Moon rotate? It does — but it's tidally locked to Earth, so the same side always faces us. That's why we always see the same "face" of the Moon and never its far side from home. Eon even asked an AI to double-check which way it orbits — a smart way to settle a question instead of guessing.
Try it
If a keyframe at 0 seconds says 0° and a keyframe at 2 seconds says 180°, what rotation is the object at 1 second? (Halfway — about 90°. That's interpolation doing the in-between math for you.)