## Geogebra Applet: Simplified Model of the Path of the Moon around the Sun

Just a bit of fun. Click the picture below to open the link. Note that the applet is not scientifically accurate – just mathematical artwork put into context.

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### 5 Responses to Geogebra Applet: Simplified Model of the Path of the Moon around the Sun

1. Ed says:

Fun fact: the moon’s path is actually convex!
(Also, I’m pretty sure that a moon will never go retrograde. I could be wrong.)

2. Ed says:

(I was wrong to suggest that moons’ orbits can’t go backwards: Io orbits at 17km/s around Jupiter which only makes 13km/s around the Sun)

3. Hi Ed, I was surprised to read your second comment. I really didn’t think that could happen – every day’s a school day ðŸ™‚

• Ed says:

That was my thinking too: I supposed that a moon overtaking its parent body would have escape velocity relative to the Sun. But that’s wrong: firstly, because any moon must overtake, and secondly, because the moon is of course inside the planet’s gravity well as well as the Sun’s.
It became clearer when I considered that the planet’s speed around the Sun depends only on its distance. We can dial up the planet’s mass as much as we like, and also dial down its moon’s distance. For confirmation, I had a look at the closest moon of the largest planet!

4. Bob Mrotek says:

Thank you for this. Twenty years ago or so I read in a book that the orbit of the moon is always concave to the sun but I could not visualize how and when I saw your applet I had a great sense of euphoria. Now I understand and I am extremely delighted!