why we can’t see air

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I understand the N2 O2 are very small molecules. But aren’t they all packed down on the earths surface? There’s no vacuum here so all of space on surface level should be filled with N2 C2O and O2

In: Physics

We can see air; it’s blue. That’s why the sky’s blue. That’s why mountains that are far away look blue. You’re seeing the air in between you and the mountain.

The molecules in air are quite spaced out, as it is a gas. Sure, gravity compacts them a bit, but they’re all bouncing around as fast as a bullet and that’s easily enough to keep them from packing fully together.

Even without that, liquid O2 and N2 are both more or less transparent, so…

The different elements and compounds that make up air are translucent, i.e. they don’t reflect any parts of the visible light spectrum. Light is still subject to refraction and dispersion as it enters air though.

I think you’re looking at the question from the wrong angle. Imagine a scenario where we only saw in wavelengths of light which were opaque to O2, N2, etc. What would you be able to see? You’d be in a literal fog cloud your whole life. You’d be effectively blind, except that you spent energy developing useless eyes, so it’s worse than being blind. Being sensitive to the spectrum we are sensitive to lets us see things other than the air that might be more important.

The air particules are of a size that doesn’t interact with the wavelengths of light our eyes use, because evolution, to create sight.

Ultraviolet/]infrared do much more than what we see, the world isn’t opaque in large distances because of the way our eyes work

Transparency is not necessarily a function of density or volume of the stuff you are trying to look through.

Water is transparent so is glass and all sorts of other stuff.

Most of the time the “seeing things” for transparent stuff comes from where there is a boundary between one substance and another.

You an see the surface of water, but you can’t really see water as such when you are submerged in it. You are always submerged in air.

Our eyes evolved to be able to see things. So we ended up seeing things in the part of the spectrum where there was both a lot of light and where air wouldn’t be too much of a distraction.

If the part of the spectrum we saw was shifted more in the direction of ultraviolet, we wouldn’t be able to see though glass for example. The microwaves that you use to heat your food go though all sorts of stuff, but are absorbed by water.

What is and isn’t transparent at what wavelength is complicated. Having more of it works most of the time. You can only see so far in water and air starts looking blueish if you stack up enough of it, while thin sheets of normally opaque material can become at least translucent.

There’s a lot of air, yes. But it doesn’t really interact with air that much at all. For you to be able to see an object or matter it has to reflect light and absorb some of the light to create color.

Like, you know how white is made of red, green, and blue? Lets say you have a red brick, it gets hit by white sunlight, it absorbs the green and blue, and bounces the red light back at your eyes. That’s how you see a red brick. The more of the light it bounces off, the better you see it.

But then there are some things that are transparent. They reflect some of the light, but they also allow some light to go through. Like glass or water, for example. You can see glass and water because they reflect a small amount of light (and because the dirt on or in them reflects a bit too), but you can still look through them for the most part, and see stuff behind or inside of it. And in this case glass is a lot more transparent than water. (it interacts with the light less) because you can see pretty much as far as you want through and inside of good quality glass, but you can only see a small distance through water, because it’s less transparent, and if you have enough of it, it will eventually absorb all of the light, letting you see nothing.

Air, on the other hand, is extremely transparent. It barely interacts with the light at all. So it doesn’t reflect enough light for your eyes to be able of detecting it. But there is, however, indeed a lot of air, so it is possible to see the effect. This is the sky being blue, and the stars being invisible during the day. That’s all that air in the atmosphere reflecting the tiniest amount of blue light down at you from the sun to make the sky look blue, and enough to drown out the light of the stars.