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Old Mar 25, 2004, 4:26 PM   #11
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this is my first post but I found it too interesting to pass up...

To revisit the initial question I would also suggest reading Steven Hawking. Light does exhibit properties of matter and energy simultaneously.

To add to 'slipe' s comment on red shifting -this is off topic but is relevant to photography in a couple of ways -one is that light is a spectrum of colours (RBG -as opposed to CMYK). One side of this spectrum, reds and oranges, are more suseptible to space-time curvature. When light passes by the earth the red side of the spectrum is 'shifted' or bent slightly which produces the red-orange sunsets and sunrises and the ideal lighting environments for photographers.
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Old Mar 25, 2004, 5:34 PM   #12
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The way I understand it, coopdujour, is that the earth's atmosphere absorbs some light. The sky is blue because the higher energy, higher frequency blue rays are able to cut through the atmosphere, but the lower energy red waves are absorbed. Eventually, the blue light is scattered into the atmosphere, making the sky blue. At sunrise & sunset, there is more air to go through, so even the blue light is absorbed, and the blue does not overpower the other colors, so the reds show through better. Atmospheric coloring has nothing to do with the red shift.
The red (or blue) shift is the light equivalent of the doppler effect. When a light-emitting object is moving toward you at a high speed, the light waves in front of it get piled up closer together, making a shorter wavelength and therefore a bluer light. When an object is moving away at high speed, the wavelengths get streched out behind the object.
Using spectrum analysis, we can see a star's light and determine the chemical composition and color temperature. Edwin Hubble noticed that galaxies far away from us were redder than they should be, indicating a red shift. This means they are moving away from us. Furthermore, he discovered that the further a galaxy is from us, the faster it is moving away. So this is how Edwin Hubble discovered that the universe is expanding. This discovery was cool enough that NASA named a really cool space telescope after him.
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Old Mar 25, 2004, 5:35 PM   #13
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p.s. I have read all of Stephen Hawking's books.
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Old Mar 28, 2004, 8:14 AM   #14
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A simple experiment you can do to understand the red shifting of the sun and moon through the atmosphere is to put a drop or two of milk in a clear glass of water. If you shine a light from the side of the glass the milk appears blue because the milk scatters blue light. If you look at a light through the glass it is a warmer color because the milk is scattering the blue out of the light passing through. The atmosphere does the same thing but over greater distance. Gravity isnít involved.
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