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Shadow Test

PostPosted: 09 Feb 2010, 16:56
by highflyertoo
I went out to the backyard and did a shadow test.

I used a limestone rock and a upside down pot plant plastic holder. I placed them both side by side at a distance of about 12 inches from each other at 4:40 pm today and noticed that the two shadows cast, DID NOT run paralell to each other. They were moving in different shadow angles to each other.

So the moon photo's of the Astronaut and Rocks that have two differring shadows is acceptable. But I don't know if they ever landed on the moon,I'm only saying that my backyard experiment in the afternoon Sun was sufficent to know that it is possible for two shadows to be differring from one another when under the one source of LIGHT to cause the differing shadows cast.

So there :D

Re: Shadow Test

PostPosted: 26 Feb 2010, 23:31
by Nostradamus
Well done. The empirical method is alive and well here at the forum.

The shadows should be parallel since the sun is far away. On the other hand the sun is not a point source in the sky. It has a readily apparent disc about 1/2 degree in size. That changes the shape of the shadows and leads to shadows having a dim zone around them - a penumbra.

There is an interesting effect with penumbra in which the shadow of a mountain always comes to a point regardless of the shape of the mountain top. A pointy or flat mountain and even a mountain with multiply craggy summits is seen to have a pointy summit if tall enough relative tot he surrounding area. This effect is due to the penumbra and the projection of the shadow onto a curved earth.

That's an interesting observation because I would have expected to see parallel shadows.