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The Path of the Moon

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Edited by Richard Walker, Thursday, 13 Feb 2025, 23:51

We know that from a Sun-centred point of view the Earth goes around the Sun and the Moon round the Earth. If we could magically hover above the plane of the Sun-Earth-Moon system, remaining at rest relative to the Sun, what would the path of the Moon look like from that vantage point?

Intuitively I thought it would trace a loopy path, something like the dotted trajectory in my sketch below.



I was surprised to find out how wrong my intuition was. The actual path is like the one below, which was generated by an nice simulation from the University of Colorado [1].


This is not to scale of course, the diameter of the Earth is about 8,000 mi and the distance from the Earth to the Sun 93,000,000 mi so if the orbit were drawn to scale your screen would need to be (roughly) 40 m wide, or the Earth drawn so small it would be a speck.


[1] https://phet.colorado.edu/sims/html/gravity-and-orbits/latest/gravity-and-orbits_all.html

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