I was surprised to learn that scientists have yet to solve the secret of why the moon looks larger when rising. Years ago, I was told by a teacher that the moon looks biggest when rising (or setting) because the observer is looking through more atmosphere, and thus its light is scattered more, changing its color and its apparent size. I have observed that this effect is amplified during very dusty atmospheric conditions. Not only is the moon affected–planets also appear larger when rising.
As a former professional photographer, I can tell you another reason that the moon appears larger at times. Our minds pan out or in trying to get usable information. Place a building near the moon, and our mind crops out all the background, seeing only the building and moon, with the moon taking up an enormous space in our processing. Place a moon in an immense background of stars, and our mind, looking for interesting things, spreads out and the moon becomes very small in the whole picture.
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The explanation of the illusion also helps explain another phenomenon, the “big sky” of the Western plains.
The big-sky phenomenon seems to require three conditions: a clear view to the horizon with but a few terrestrial details on the horizon, fine detail in whatever clouds are present near the horizon, and low-humidity, high-visibility conditions. After reading the article, I realized that the comparison of the distant atmospheric objects with the distant terrestrial objects makes the atmospheric objects look further away, thereby making the sky look bigger.
I have been fascinated by this illusion for 35-plus years. One thing that doesn’t fit the conclusion is that if you turn your back, bend at the waist, and look at the moon between your legs, the moon appears to be smaller on the horizon. Sounds funny. I thought so until I tried it.
I hope the illusion continues. Life should have some mysteries.
Hugh M. Black
The illusion also occurs when observing a jet aircraft contrail that starts near the horizon and moves toward the observer. The trail appears to be standing on end vertically (similar to a rocket launch). However, the “top” of the column is obviously much closer. The unusual quality of the illusion would have been been further emphasized had the author stated that the overhead moon is 4,000 miles (one Earth radius) closer to an observer than the rising moon.
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If this article is not a joke, then someone should advise the author to test the reference theories while 50 miles out to sea. It will not hold water there, either.
Stone Mountain, Ga.