The sky moves two ways at once, in opposite directions. Almost every confusion about charts starts here.

This page is a seed. The full write-up is coming; for now it exists so the links that point here resolve, and so the shape of the codex is visible while it grows.

what belongs here

  • what is physically happening, in plain language
  • what it moves, and how fast
  • which techniques are built on it
  • the beginner confusion it clears up