The Bedtime Scientist

Episode guide

Moon Phases: Why the Moon Changes Shape

The moon never changes shape; the light on it does. This episode watches a whole month of moons and finds the pattern hiding in plain sight.

The science, gently

  • The moon makes no light of its own; we see whichever half the sun is lighting.
  • A full cycle of phases, new moon to new moon, takes about twenty-nine and a half days.
  • The same face of the moon always looks at Earth; the far side is not dark, only private.

Wonder together

  • What phase is the moon in tonight? Can you name it?
  • Why do you think people used moons to count months?
  • If the moon kept a diary, what would this week's entry say?

Tonight's calm-down

Whatever slice of moon is out tonight, it is the same whole moon, patient behind its shadow. You are whole in the dark too. Wax and wane your breath: fuller, thinner, fuller, thinner, gone.