Why does the sky look like a dome?

I mean, it’s not as if it’s a solid, curved object.

Thoughts, anyone?

[del]I think it’s the same optical illusion that makes the moon look larger near the horizon: you see it next to stuff you know is (relatively) close by, so you perceive it as closer, too.

WAG quotient: 65%.[/del]

Here’s the illusion I was referring to. Seems I got it exactly backward, so nevermind. :rolleyes: at myself.

I question the premise of your inquiry.

I don’t think the sky does look like a dome.

I think the WAG quotient is way higher than that. I tried running it through my WAG meter to check, but Gay Deceiver refused to let me as she was afraid of an overload.

What else would it look like?

Put it this way - you look at the sky. It seems a certain distance away. You look at a different point in the sky. It seems the same distance away. You keep on looking, and everything above you appears to be the same distance away. What architectural element consists of walls located an equal distance from a single point below them? A dome.

It occurred to me that others may not share that perception. I’ve heard it used many times, though, and I’m all-but-certain it was a common belief in the ancient world.

That response is annoyingly plausible.

I aim to displease.

I really do need to get my meter calibrated. Be sure to note my edit above.

Given that your meter only read 65% on said response, you’ll probably have to replace the motherboard, buy all new sensors, and basically replace everything but the wrist strap. It’ll be easier to buy a new one. :smiley:

Hey, here’s good news! TigerDirect has them on sale!

Sorry, but I always check the bottom of the window before I click a link.

It may not be solid, but the sky IS curved. Gravity makes the atmosphere into a hollow spherical shape with the hollow filled by the earth. A section of a sphere when seen from below (where we are when we stand on the earth) is … a dome!

So… it looks like a dome because that’s what it is. It just happens to be a dome made out of gas rather than bricks or stones or plaster.

Maybe you should ask why it doesn’t always look like a dome when it is?


Poopy head.

Think of it this way. In space the “sky” looks like a sphere. It surrounds you. It’s like being in a giant starry hamster ball. It’s everywhere you look and everything looks the same distance because the space between your eyes isn’t wide enough to depth precept stars trillions of miles away. What’s the geometric figure that each side is the same distance from the center? A sphere.

Now on earth the ground blocks half the sphere so you can only see half at best. That’s the dome.

Just because I no longer threaten you guys with flying monkeys doesn’t mean I can’t be frustrating.

Plus that joke was old back in third grade.

You realize that Alessan said pretty much the same thing, right? :slight_smile:

I’ll go further, and say that the sky not only looks like a sphere, but that it actually is. The sky is basically just the set of all directions in three dimensions (or, depending on context, the set of such directions which do not point to some portion of the Earth), and that set has all of the geometric and topological properties of a sphere (or hemisphere). So it looks like a sphere because it is one.

A surprising amount of upper-level physics boils down to accepting that many things really are as they appear.

Yea I got too excited and posted without reading; usually a mistake but Chronos’s post was interesting so if it set that up then it isn’t a total loss.

Your eyes focus light in the same manner a camera does. If you look on the side of a manual focus lens it will have a scale showing the distance that your focal plane is from the camera. The scale is logarithmic (?) where the distance rapidly increases from one meter to two, then five, ten, twenty… and then infinity. I have a wide angle lens that has just three marks: 0.5m, 1m and infinity. Focus wise, that tree at the end of the block is the same distance as the Andromeda Galaxy. So, when you look up in the sky everything is the same distance away-infinity.

Except the crap they put on the tests that accounts for 90 percent of the grade! :slight_smile:

Back to the dome thing.

IIRC “they” have figured out the human brain really doesnt see the sky as a proper dome, where the distance from you to the dome is the same whether you look straight up or towards the horizon.

Its more like an oblate spheroid, or some other exotic shape.

Your brain percieves the stuff ABOVE you to be closer in physical distance than the stuff on the horizon.

Hence the full moon illusion, in which a full moon on the horizon looks bigger than when its straight above, even though its for all practical purposes the same distance away. The illusion also works for constellations, though IME seems more pronounced for the smaller ones.

Why would that be? The moon has the same APPARENT size whether its on the horizon or straight above. Ahhhh, but your brain “remembers” that stuff above is closer than stuff towards the horizon. IF something has the same apparent size, then stuff towards the horizion would HAVE to be physically bigger.

Think about it. EONS ago, stuff that was important to humans above was pretty close. Trees and the stuff in them. Stuff towards the horizion was physically much further away. Not surprising that that knowledge could be genetically hardwired into our brains.

I’ve found I can defeat the moon illusion by looking at the moon (or small constellation) at the horizon when bending over backwards. Though, now the thought of it makes my back hurt and makes me queasy.

Sometimes an picture is worth 1000 words. A google image search of [earths atmosphere](http://images.google.com/images?hl=en&q=earths atmosphere&um=1&ie=UTF-8&sa=N&tab=wi) comes up with a few images like this, this, or this which might help with mentally picturing the answer.