Naked Science Forum
General Science => General Science => Topic started by: Quantumcat on 15/12/2003 17:51:14
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Can someone tell me, why, a week ago, at about 6.00pm or so the moon was huge really orange/yellow and near the horizon, then at midnight when I looked out my skylight it was really high in the sky, normal size and white.
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I would assume that it has something to do with the way light scatters in the atmosphere. It may have been caused by a similar effect that makes the sun look orange near sunset.
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It's to do with the same reason we discussed on QOTW a few months ago about "why is the sky blue and the horizon red when the sun sets ?".
The atmosphere scatters light of short wavelengths (i.e. blue light) to a much greater extent than longer wavelength light - like reds and yellows. The effect is exacerbated by dust and pollution in the air which tends to scatter light at the red end of the spectrum.
This means that when the sun, or in your case moon, is on the Horizon the light is passing a much greater distance through the atmosphere so more of the blue light is scattered leaving light enriched for red and yellow wavelengths, making the moon (or sun) look redder on the horizon. If there is pollution in the sky the reds get scattered, making the moon look more yellow. As the moon climbs in the sky, away from the horizon, you see a white moon because the light it is reflecting towards earth passes through much less atmosphere to reach your eye and so less is scattered on its way to you.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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Okay, so that's why it was yellow but why was it huge and near the horizon, then moved high in the sky in only a couple of hours? I remember when I was little I watched a lunar eclipse, the moon turned yellow then red then disappeared. Was there a lunar eclipse a week ago? Did anyone else see it? :P
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The moon on the horizon is a well known optical illusion. The moon looks bigger when it i lower in the sky because there are other things in view for your brain to compare with the moon - trees, buildings, pylons etc.
But once it rises high in the sky there is nothing for your brain to compare the moon with and so it looks smaller.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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Also, because the top of the atmosphere is curved, there is a lensing effect on light (or other electromagnetic waves) that pass through it. When the moon or sun appears very low to the horizon, you can see this effect more than when they are higher in the sky, because the waves are passing through more atmosphere. Under certain circumstances, this effect can actually allow you to see (or a satellite receiver to "see" the satellite) a little bit below the horizon. About 1 to 2 degrees if I remember correctly. There is a higher magnification vertically than horizontally, so things look somewhat distorted.
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John
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oooh interesting. how fast does the moon usually travel in the sky?
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I don't really remember how fast the moon travels. It takes about 28 days to orbit the earth, and exactly the same amount of time to rotate once on its axis, thus it always keeps one face toward the earth. With the earth's rotation, I seem to remember that moonrise is about 20 minutes different each day (but I may be off on this). So, it is visible in the sky almost as long as the sun is during a day.
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John
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hi quantumcat
the answer to your question is very simple.
1. shorter wavelengths get scattered much more than longer wavelengths.. visible region which we are seeing is from 0.4 micrometer (blue) to 0.7 micrometer (red). blue light is scattered much than the red and so the moon or sun looks red .
2. as the path of light ray to travel is more scattering is more , which causes most of the shorter wavelengths to scatter and longer wavelengths pass through.
3. this effect is due to the MIE SCATTERING AND NONSELECTIVE SCATTERING.
Groucho Marx also has correctly stated. if you can't still understand , contact me.
hi iam a student of geology and currently doing my post graduate degree in remotesensing
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Recently, I read an article about sulphur. It said that when sulphur is heated it changes from a yellow solid then pale yellow liquid then suddenly thickens and becomes dark brown. Jupiter has that orange brown colour is due to the heating of sulphur particle in its atmosphere. Do you think the orange moon Quantum saw could be due to this?
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