Big Sky

Oak Creek, Arizona
34 47.33 N 111 47.09 W

We are having a wonderful time with our friends John and Mary Ann. We have missed then since they moved to Arizona, so this is a time to catch up. They have been treating us to the natural delights of the Sedona area. No matter which direction you look here, you see beauty.

Sedona's famous Castle Rock

Mary Ann, Libby and some neighbors go hiking.

But even before our arrival here, Libby and I began talking about the big sky effect.   In case you don't know, when you come to areas like this, the sky appears higher and bigger than in other places.   It is as if the sky were a big blue dome over us, and that we could perceive the size of the dome to be different in different places.

We know it isn't just us imagining it.  Almost everybody notices the effect.  Indeed, the state of Montana calls itself "Big Sky Country"    

The sky in the American West, seems bigger than in the East.  The sky in Sweden seems smaller.  The sky at sea seems smaller regardless of longitude and latitude.   They sky in Alaska? (we don't remember).

What is this big sky thing?   Is is imaginary?  Is is a physical effect?  Is it an optical illusion?  I tried to research it on Wikipedia; nothing useful found.  I searched the question on Google.  I found surprisingly little; only a couple of posts where people asked why big sky, and the answers they got were amateur and non-scientific.

Here's what I think we know.

• It is not merely a question of latitude.   Montana is far north of Arizona.  In the lower 48 states of the USA, big/small sky seems to be more of an east/west phenomenon than a north/south one.
• It is not merely a question of scenic vistas.  In the West, from elevated locations one can see many 10s or even hundreds of miles.  In the East, views are mostly blocked by trees.  At sea, the horizon is uncluttered and uniformly 3 miles away when we stand at the helm.
• It does not seem to change with season or time of day, therefore the height of the sun in the sky is not the answer.
• It seems to apply equally if the vista is flat desert or soaring mountains.  From a mountain top in Vermont, we can see 100 miles.  From a mountain top in Arizona we can see 100 miles.  Yet the sky appears bigger from the Arizona mountain top.

So, what is the real answer?  I don't know.  Maybe you do.