[anyqs] Speed Of Light

Here’s another. Again, these are push-ups to me. If I don’t make an exercise out of turning interesting things into challenging things, the result is that I become less interested in things altogether. Here’s the original thing that interested me.

  • h/t Max Goldstein who brought the original animation to my attention. I’m fascinated with his fascination with the dimensions of the Earth’s atmosphere in pixels. If I were to rank the things about that animation that fascinate me, I’m not sure that datum would crack the top fifty. There’s a lesson for me in there somewhere.
  • Here’s something that kinda sorta looks like I’m trying to make a lesson plan out of this video.
  • While we’re on the subject of #anyqs, I love this effort from Mylène at Shifting Phases. She dips her toes in the #anyqs waters and makes a huge splash.

2011 Sep 06: I posted this #anyqs for response to Twitter and got a long, resounding “Huh?”

@thescamdog: @ddmeyer I've got nothing. Mostly I wonder what the shady looking guy with the flashlight is up to.

@park_star: @ddmeyer had to watch it twice and i'm still sort of wondering what the heck is going on.

It should go without saying that this kind of feedback is just as valuable as the kind where everyone aligns around the same question. Far better to get this feedback now, on Twitter, from a group of math educators, than when it’s too late, in the classroom, from thirty bored math students.

I'm Dan and this is my blog. I'm a former high school math teacher and current head of teaching at Desmos. He / him. More here.


  1. When I looked at the video, and saw the circles on either side of the video, I was unsure what they represented, but I noticed that they were of different sizes. My assumption, once you shown the light upward, is that you wanted to compare the difference between light travelling instantaneously between Earth and the Moon, and light travelling at the speed of light instead, in which it takes a measurable amount of time for light to travel between the Earth and the Moon.

    Explaining that light has a speed, and that despite our common sense judgement that it travels instantaneously fast, it actually travels much slower, is quite a difficult thing to do. The problem really is that at the scales we are used to dealing with on an everyday basis, light IS essentially instantaneous.

    I think, in order for your video to work, students will have to understand a fair bit about light & distances between the sun and the moon to be able to even see the question that is being asked. I would imagine that your video poses an interesting question for students in an upper high school level or 1st year university physics course, which is not a bad target market.

    I wonder if a game could be written which actually took the speed of light & relativistic effects into account, and allowed students to play around with the idea of a maximum speed of light at more human comprehensible scales, would help people understand these concepts more deeply than the ability to manipulate the formulas and get “the answer.”

  2. “What are the dots?”


    David: the first one isn’t quite instantaneous. Its just much faster.

    I think you’re right that the speed of light is a tough concept, but what I find more difficult is to fully grasp the vast distances in astronomy.

    Ask anyone to try to draw the Earth and Moon to scale, along with their to-scale distance. How many will come remotely close?


    Ok, I have a new question. “How long is the second beam of light?” 7 light seconds?

    Actually in just looking this up… that means the 2nd dot is not the moon. What the heck is 13 light seconds away from Earth? Whole lot of nothin!

    And the first dot? Too close for the moon. ISS?

  3. p.s. I was looking at this question in my pre-calc text and they just reduced it into plug’n’chug.


    I felt they were asking things backwards too. We didn’t know the speed of light when we were asking “How far is the Sun?” And we’re just given the Moon’s distance? How droll.

    What kind of prompt lets our students ask,
    1. “How far is the moon?”
    2. “How big is the Earth?”
    3. “How far is the sun?”
    4. “How big is the sun/moon?”

    #2 is in Michael Serra’s Discovering Geometry. But the “real” solution to it involves travelling to the equator :)

  4. Thinking as a student and not a physicist, we can see light from the sun and stars because they are BIG, so it makes sense that we can see their light billions of miles away.

    But if a star is so far out there it is possible that we can’t see the light. With that said, is a house hold flashlight intense enough to be seen from the moon?

    With that said, does ANY light from that flashlight reach the moon, even on a clear night?

    Something here seems anti-intuitive for me that doesn’t seem to meet Dan’s three-act theory.

  5. I saw a couple of dots and a guy playing with a flashlight. There was nothing in the video that suggested the speed of light–only the title for the blog post.

    Sorry, this one evokes nothing but boredom for me.

    Even after an explanation, it is dull.