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Originally posted by ArMaP
It's not oxygen that makes the sky blue, it's the fact that the atmosphere is dense enough for scattering the light.
According to this, if a planet has a thinner atmosphere it should have less scattering, but it will still have some, making the sky a lighter blue.
All of this if I am not wrong, this is the idea I have about it, but I may be slightly wrong.
Why is the sky blue? Parents and teachers have traditionally made up lots of reasonable explanations. Adults are supposed to know the answers to such simple questions, right? Unfortunately, all of the explanations that I have ever heard are at least partly incorrect.
The correct answer is: Only because of a remarkable coincidence.
The Earth's atmosphere is primarily made of Oxygen and Nitrogen. It happens that both these are made up of atoms of about the same size. It also turns out to be true that EVERYTHING has lots of empty space between and around the atoms that it is made of.
Our Sun produces light which is actually a mixture of light of a lot of colors (called a spectrum, another subject). You can prove this with a prism, which separates the colors of what we normally call white light or sunlight. These various colors are actually just different sizes (wavelengths or frequencies) of waves of radiation (light). Our eyes only recognize the total of all this light, and so it appears to us to be a bright yellow, almost white color.
It turns out that RED light in the sunlight is the lowest frequency and therefore is the biggest wave (yet another subject!). These big waves happen to be around twice as big as the size of the waves of blue and violet light also in the sunlight. When these BIG waves pass through the earth's atmosphere (or any other collection of oxygen and nitrogen molecules) they are not affected very much by the relatively SMALL atoms of Oxygen and Nitrogen; so most RED light continues straight on through. (They are able to go around the atoms more than bumping into them.)
The BLUE (and violet) light in the sunlight is the highest frequency (of what we can see) and therefore has the littlest waves. These smaller waves happen to be around half the size of the red waves just discussed. When these SMALL waves of blue light pass through the earth's atmosphere, many of them eventually "crash into" the relatively LARGE atoms of Oxygen and Nitrogen. They tend to "bounce off" (are reflected or SCATTERED) and then they go all directions including sideways and down toward us.
A more scientific way of saying this is to say that the Oxygen and Nitrogen atoms are of a size that has a "natural vibration rate" (called frequency) that is closer to the rates of vibration of BLUE light. So the blue light can cause those atoms to start vibrating. The vibrating atoms then give off blue light when they stop vibrating, and that new blue light can go in any direction. (It's a little more complicated than that, but the general idea is correct.)
The REALLY complete explanation of this is called the Rayleigh Theory of Scattering!
As sunlight is passing through the atmosphere horizontally above you, the RED light tends to go straight through, while the BLUE light tends to get bounced around (what is called "scattered") as described above. When you look up at open sky, you see this scattered light which is mostly BLUE.
Please notice that I keep saying things like "usually", "mostly", "tends",and not "always". Remember that there is a LOT of empty space between the atoms in the air. Some blue light CAN make it through a good distance of air. But, the farther that the light has to pass through air keeps making it more and more likely that the blue light will be scattered while a good amount of the red light will continue on through.
So it's only because Oxygen and Nitrogen atoms just happen to be a size comparable to the size of some of the waves of visible light, that the sky is blue! Neat, huh?
Q A question: If Oxygen and Nitrogen atoms happened to be a lot SMALLER, what color would the sky be?
(Answer: Nearly BLACK, while the Sun would look whiter than it does and there would be almost no dawn or dusk- it would just suddenly become day or night) The Oxygen and Nitrogen atoms would not be vibrated by any of the visible light, so nearly all would pass through, with very little being scattered by the sky. It would be likely that bright stars could be seen during the day!
Q Another question: If Oxygen and Nitrogen atoms happened to be a LOT BIGGER, what color would the sky be?
(Answer: Nearly BLACK again, with the Sun again seeming whiter than now.) The Oxygen and Nitrogen atoms would again not be vibrated by the various colors of the visible light, so again, all would pass through.
Originally posted by spookjr I very seriously doubt Carl Sagan would have stood by and perpetuate an obvious fraud.
Originally posted by zorgon
reply to [url=http://www.abovetopsecret.com/forum/thread324816/pg20#fo NA
Underground submarine bases, scuba diving under Death Valley to see rare fish...
Again, not aware of that, sounds interesting, do tell...
I am going to find those darn Rovers..... they just have to be out here somewhere...
[edit on 30-7-2008 by zorgon]
Originally posted by Dan Tanna
I love this picture. Martian landscape looks alot like earth.
I will have to have a good hunt for the origional.
Originally posted by Fulcrum29
Well ladies and gentleman as of an hour ago it is official Mars has water according to Nasa:
next step is to search for life.
Seems we're out step away from life on mars and disclosure.
Originally posted by Misfit
I am not trying to cross-thread, but ..........
I thought this was a couple/few months ago? Not speculation, but confirmation from NASA that water was indeed found?
Should I pack my bags and go to that timeline thread? I do admit that I adamantly remember Billy Graham dying. And I sure as hell remember the NASA/Mars/water disclosure.
Originally posted by fleabit
Finally, NASA, if they were covering things up, would not make such huge blunders as to put pictures on their site for the general public to view, if it contained things they wanted hidden.