From the February 2018 issue

What’s “overhead”?

Looking straight up may be harder than you think.
By | Published: February 28, 2018 | Last updated on May 18, 2023

Recently, I went outside for a walk and casually noticed that the Sun was about one-third of the way up the eastern sky. Or was it? Out of curiosity, I noted the time and later used software to determine that the Sun was actually only 17° high at that time. How could I have been so far off?

Part psychology, part physiology?

In Light & Color in the Open Air, Marcel Minnaert helps us to understand why it is common for us to overestimate the heights of objects in the sky. It stems from a psychological effect in which we naturally perceive the hemisphere of sky as a flattened vault that appears about twice as close overhead as it does to the horizon. If you try to estimate the midpoint between these two points, the result will not lie at a height of 45° but generally somewhere between 20° and 30°.

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