This Is What Happens When a Physicist Reads "Goodnight Moon"

By Eliza Strickland | October 18, 2010 1:54 pm

goodnight-moonGoodnight moon, goodnight room. Goodnight frogger, goodnight super-analytical blogger.

Chad Orzel of the physics blog Uncertain Principles has had plenty of time to contemplate the beloved children’s book Goodnight Moon in the course of bedtime readings with his toddler. And he got to wondering, just how long does it take the book’s bunny protagonist to say goodnight to all the objects in the room? And could a physics blogger figure it out from eyeballing the moon’s rise through the sky during the course of the story?

Happily, yes. Go read the full post for the math of the moon’s passage through the sky; we’ll skip to the results and tell you that Orzel puts the figure at about 6 minutes. But there’s a hitch: The clocks shown in various pictures of the bunny’s room instead show that one hour and 10 minutes have elapsed. There are only two possible explanations, Orzel says:

These two methods clearly do not agree with one another, which means one of two things: either I’m terribly over-analyzing the content of the illustrations of a beloved children’s book, or the bunny’s bedroom is moving at extremely high velocity relative to the earth, so that relativistic time dilation makes the six-minute rise of the moon appear to take an hour and ten minutes.

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  • Nemesis

    Would it actually be: “relativistic time dilation makes the 1 hour 10 minute rise of the moon appear to take 6 minutes” instead of the other way around?

  • sam

    Actually, the house need only move along the Earth’s surface at a speed slightly less than the speed (in revolutions) at which the moon orbits.

  • Brian Too

    Orzel has (understandably) missed a 3rd possibility.

    Who says that the story is from Earth? Maybe it has been “translated” for human readers, and the Moon is a moon from another world…

    That could explain a shorter lunar orbital period.

  • paul

    Yeah, time dilation would work the other way, but simple motion could keep the moon wherever you want. The other obvious choice is that the pictures display a subtle shift in viewpoint, so that the apparent motion of the moon is affected by parallax. (Or the house is on some kind of tippy foundation, so the the view out the windows changes even while the viewpoint inside remains the same.)

    Landslide house!!!

  • Bella Rossi

    Does anyone have the absolute answer?

    Bella Rossi


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