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Light Refraction In The Atmosphere

Sun Jun 05, 2005 1:44 pm

I was wondering: water bends light...if I stick a spoon in a bowl of water it looks like it is bent...water is in the atmosphere...if the moon looks like it is 40 degrees above the horizon, is that really where it is...or is the image of the moon refracted and the moon is actually at 30 or 45 or whatever degrees above the horizon but appears to be at 40?

Thanks for any responses

(maybe Logan22L can answer this because he has a laboratory Big grin )
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RE: Light Refraction In The Atmosphere

Sun Jun 05, 2005 5:11 pm

I'm not an expert on this by any means, but from what I remember, you can still see the sun for a few minutes after it has set because the light is being refracted around the curvature of the earth by the atmosphere. I believe that this is also why the sun (and moon for that matter) appear bigger or different colors when they are closer to the horizon. However, once the moon gets up into the sky, it has a more direct path to your eye, so not as much refraction occurs. The difference between apparent position and actual position is not more than a few degrees near the horizon, and probably only fractions of a degree when it's higher in the sky.

I could be way off, but that's what I remember from meterology class.

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RE: Light Refraction In The Atmosphere

Sun Jun 05, 2005 6:24 pm

Mir is right to a degree, the curvature of the Earth helps in the fact that sunlight is refracted from the top layers of the atmosphere during the final minutes of sunset, what happens is the sun will slowly go down below the horizon, not a noticeable difference in speed, but due to the refraction the sun has actually set some 3 minutes prior to what your seeing it then.
The Moon looks bigger however due to visual distortion, a different effect than Atmospheric refraction, but still intresting nonetheless.
Your eyesight "tricks" you into believeing the moon is bigger because you use visual points as references, when the moon is higher up those references are gone, thus "fooling" your brain into thinking the moon is smaller when infact its just the same size.
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RE: Light Refraction In The Atmosphere

Sun Jun 05, 2005 6:50 pm

The image is refracted and "abused" in all kinds of ways, this has a lot to do with the temperatures of the layers of air between you and the moon. Cold air is denser than hot air, so air can bend light just as easily as water can. In fact, light gets bent every time the medium it's travelling through changes density. I don't really know how humidity affects density, though.
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