# How big is the sky?

Sure, “sky” is a concept more than it is a thing. But I’m speaking generally about the layer of the atmosphere where the sun’s light is scattered into the bluish spectrum. And by “how big”, I mean in terms of length & width. How far away from zenith point (my reference) is the farthest “piece” of sky that I can see? Can I (in Washington DC) see the patch of sky that’s currently directly over, say, Nebraska? If the sky were perfectly reflective like a mirror, what states would I be able to see in its reflection?"

IIRC, the sky turns “dark” (i.e., scattering of sunlight isn’t significant to color the sky every which way you look) at about 20 miles. Not very high, atmosphere-wise. Trace gases that can be attributed to being caught by Earth’s gravity go up to 600-1000 miles.

I don’t have the figures for how far the sky you see extends. But offhand I’d say it’d only be on the order of 50-100 miles; i.e., if you look due west (in DC) and see a cloud, that cloud is probably overhead anywhere from Gainsville, VA to Winchester, VA.

“How high is the sky,
How deep is the ocean?”

Actually the sky is 4394 x 4038 but I’m not going to tell in what units.
[sup]Also that in from here, not where you are standing.[/sup]

I’m too rushed to re-do the math here, but if you follow my logic in this thread, you can calculate an answer to your question. Just for reference, 20 miles = 32 km.

Since the angle of incidence is equal to the angle of reflection, the landmass you’d be able to see reflected is simply double the distance of the farthest point in the sky you can see.

I hope that’s clear.

It’s a simple right-triangle problem. If the radius of the earth is about 4000 miles, and the “top” of the atmosphere is around 30 miles, then your line of sight towards the horizon will hit the to of the atmosphere over a distant spot, with the distance being:

SQRT( 4030^2 - 4000^2 ) = 490 miles

However, the atmosphere has an optical density gradient which bends the light, which allows you to see farther than that. But I don’t know how strong this effect is. (I’ve heard that days last longer than they should, since the sun appears to dip below the horizon awhile after it should have done so predicted by the geometry.)

And if the top of the sky was a mirror, it should let you see reflected objects from twice as far as the “radius of the sky”, or 980 miles from your location. That is, if we ignore the atmospheric light-bending effect.

On the other hand, the usual bunch of aerosol particles make the atmosphere misty. I don’t think you can see through 980 miles of air, or even 490. More like 100 miles on a good day.

In meteorological terms, visibility is called ‘unrestricted’ if it’s 7 miles or better. In cities and industrial areas, haze reduces vis to less than 7 miles frequently. I’ve occasionally seen visby remarks that say 20 or 30 miles, but only in rural areas.

BUT those observations are made by someone near the ground who is looking at objects that are (sort of) near the ground. Seeing clouds 50 miles away might be possible, but rare. 100 miles is too far.

I found a website that gives a simple formula for distance to the horizon. You can also use it to calculate how far beyond the horizon you can see tall objects. According to that formula, if a cloud is 10,000 feet high, you could see it about 120 miles away.

So from DC you could see part of the sky over Richmond, VA. You just can’t see the bottom 7000 feet of sky.

The top of a 30,000 foot high cloud would be about 200 miles away.

I guess if the sky were a mirrored dome that was 30,000 feet high, you could just double that and say that you would see a reflection from 400 miles away. (Assuming perfectly clear air.) Maybe Charlotte, NC?

Looking straight up, how far could you see? The atmosphere is about half as dense when you go up 5500 meters (about 3.5 miles). If visibility is proportional to density, (and I think it is, more or less) then you should be able to see all the way thru the atmosphere. Which just makes sense, since we can see the moon in the daytime.

Once on summer vacation at Gulf Breeze Florida, the blue of the sky extened unbroken all the way down to the horizon. It was VERY weird. Eerie even. You don’t realize how accustomed you are to the whiteness near the horizon until it’s gone. The weather was only like that for one day. I wouldn’t be suprised if it only happened once every few years.

Yep. The sky at zenith looks blue because air is a smoky-blue transparent layer viewed against the black of outer space. We know what a far thicker atmosphere would look like: look at the sky right at the horizon. It’s usually misty white, not blue, and it’s that way because we can’t see all the way through it to the black beyond

I’ve often wondered what an asteroid strike would really look like, since it probably would fling a huge gout of atmosphere high into space. The artists’ depictions never show this. A big blob of air, when viewed in sunlight against outer space, should look like misty sky-blue transparent smoke.