The Windmills of Your Mind

Tree Trails

A recent Astronomy Picture of the Day (APOD) is shown above. The point was to illustrate that star trails really are evidence of our rotation as a planet.

Are photographs of star trails really evidence of the Earth’s rotation about its axis? Yes they are, and science journalist Trudy E. Bell discovered that there is a simple way to demonstrate this, if you have the stomach for it.

Trudy Bell went to a local playground where a merry-go-round or whatever you may call it, sits underneath a tree. After being spun up she took a long exposure photo of the tree and gets an image extremely similar in nature to those seen of concentric star trails. But is this proof that our planet is spinning? I cannot decide.

I was once asked by a religous man to prove that the Earth goes about the Sun. Everything I tried to think of he dismissed as requiring some other assumption which I would then have to prove. It wasn’t that he didn’t believe it was true, but he wanted to illustrate that maybe there are things taken for granted like our rotation on our own axis that perhaps we ought to prove to ourselves once in a while.

Just because these pictures look the same though does not mean tis is the same thing. you would get just the same image if the tree rotated above the merry-go-round, wouldn’t you?

I can’t think of how to prove it – if you can then please let me know…


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