American in Spain

When I saw yesterday’s Astronomy Picture of the Day, I was fascinated by just how big the Earth’s shadow is on the Moon. When I made a comment to this effect on Facebook, my friend, Josh Grady, said, “It’d depend on the distance between the two, no?” Of course the size of a shadow depends on the distance to the object its cast upon, but I hadn’t considered that the distance from the Earth to the Moon varies, due to its slightly elliptical orbit around the Earth-Moon barycenter, by 42,840 km, causing it to appear 12% smaller at its apogee than at its perigee. This raised the question: What are the minimum and maximum sizes of the Earth’s shadow on the Moon?

To the geometrymobile!
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Last weekend, we had a thunderstorm come through. They are way more rare here than in my native North Carolina. We also have two new cranes that have been put up next to our house to build even more housing. Intrigued by the idea of two visible metal cranes towering into the sky and a coming electrical storm, I set up my camera to record out the window.
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