domenox wrote:But then, I got to wondering maybe a digital camera would be able to answer whether the sky is "actually" blue and rule out the hypothesis that our eyes are a big factor when it comes to seeing blue skies? Couldn't the data corresponding to pixels of a blue sky be compared to the data corresponding to a sample violet pixel and could this then answer whether a sky is "really" blue or we're just perceiving it wrongly as blue due to our eyes' limitations? (I'm not knowledgeable on cameras or optics or anything so just tell me if I'm missing something obvious here like for instance maybe digital cameras are created to match our eyes' color judgment abilities or whatnot.)
That would amount to the spectrograph seen here, if I understand you correctly:
stianhat wrote:The sky is blue because of the colors it *lacks* not the colors it has - we percieve chlorophyll filled leaves as green because they lack the red light and correspondingly, as someone was close to earlier, we see the sky as blue because it lacks red light, but also has violet light ( violet = not yellow ) (not red = green). the resultant mix of (not yellow) + green = blue. The blue light that is already there just adds to this.
red and violet light such that the only light it reflects is green, which we perceive. But the sky is blue because the blue end of the spectrum is more widely scattered than the other wavelengths. The color wheel doesn't really get into it, I think.
Harry Voyager wrote:Nitrogen is colourless, so the oxygen is a diluted dye. The atmosphere is also 11km deep, and 5*10^18 kg, so if I've done the numbers right, if you are standing on the ground, looking straight up at space, you are looking through something like 40 gigatonns of atmosphere. Even a very dilute dye can acquire an intense colour when you look through enough of it.
Let's put it this way, then: why is oxygen blue?
It is hinted in http://www.youtube.com/watch?v=WuG5WTId-IY
, posted earlier, that the color of liquid oxygen
results from the solvated, unpaired electron. A better example would be the Birch reduction
), in which sodium (and its easily-removed outer electron) is dissolved in liquid ammonia. Basically, the molecules align in such a way as to confine the movement of the electron, and the confined electron can absorb the relevant wavelengths of visible light to reach an excited state.
But in its gaseous state, the oxygen molecules would be too far apart to confine an electron in a similar way. So why would oxygen be blue? If I am not mistaken its absorption spectrum lies entirely beyond the visible range.
EDIT: Okay, that sounded plausible, but a little more Googling suggests that isn't right either. http://chemed.chem.purdue.edu/demos/mai ... /14.2.html
puts it quite plainly:
A single photon carries enough energy to excite two O2 molecules simultaneously. This transition is not observed in small amounts of oxygen gas at low pressures due to the very low probability of this three-body process. In the liquid, however, this transition is rather common because, as a general rule, the volume of a gas decreases by a factor of about 800 when it forms a liquid.
More to the point, even the Wiki on oxygen
says it is a colorless gas (as opposed to ozone
, which is plainly described as pale blue).