How big is the Earth’s shadow on the Moon?

December 16, 2011 By: erik Category: Geeky, Math, Musings, Photos, Science

Earth's UmbraWhen 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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Naked Bulb

November 21, 2007 By: erik Category: Flickr, House, Photos

One of the first thing most visitors to our humble home say is, “So you guys got something against lamp shades, or what?” Our house still has the original light bulbs hanging from wires popping out of holes in the ceiling that the original builder left. And all the previous owners have shared our apathy about remedying the situation.
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