# Clouds..

And now, deep thoughts…

Has anyone ever wondered how far two people can be apart and still see the same cloud? I know there would be a lot of factors involved, but just on average. Say I was looking at a cloud in southern Michigan, could someone see that same cloud from Ohio? Just a thought…

It’s 11:30 pm central time on a Friday night. Don’t you have some drinking to do, or is that sort of thing that prompted this question?

I don’t have an answer, btw. But I’m guessing the Michigan - Ohio thing is a bit far-fetched. Don’t most planes fly above clouds? I’m sure you can’t see a plane from one city to another, but then again a cloud has size on its side. I’m still guessing though, that an individual cloud can only be seen in say, a 30-40 mile radius.

The highest cloud-tops listed here reach 9+ kilometers. So if we just use 9 for convenience and add that to the Earth’s radius (6378 km), a tangent drawn from that point to the Earth’s surface will cover an arc of 3.04° ( cos[sup]-1/sup ). A bit more math yields a land distance of 338.6 km, or 210.4 miles. So theoretically you can see a cloud, just above the horizon, that’s 210 miles away. Of course, atmospheric haze - not to mention trees, buildings, etc. - cuts that distance way down in practice.

Hey! I was only about 140.4 miles off! Ever better if I lie and claim I was taking trees, hills, atmospheric haze, etc in question…

[Winnie the Pooh]How sweet to be a cloud
Floating in the blue!
Every little cloud
Always sings aloud.[/Winnie the Pooh]

Crunchy, I’ll be nice today and cut you some slack. If, to clear land obstructions, we say that a cloud has to be at least 10° above the horizon to be visible, the arc on the Earth reduces to a mere 0.45° (law of sines), which translates to a land distance of 49.9 km, or 31 miles.

Now, also notice that these calculations are based on the highest cloud-tops. If we use a height of, say, 10,000 ft., (3 km - completely arbitrary, but seems reasonable), then the “horizon-view” distance is 195.6 km, or 121.5 miles, and the “10°-view” distance is a scant 16.9 km, or 10.5 miles.

So does this mean these people have looked at clouds from both sides now?