Hacker News Reader

Comment by calinet6 | Hacker News Reader

I always thought it was a very simple relative size illusion. When placed next to objects on the horizon that provide a relative measuring stick of size, we perceive the moon as large in comparison. When the moon is high and we instead have a vast and large sky free of landmarks to use as subconscious or conscious measuring sticks, it appears comparatively small.

There is a lot of cognitive function in-between, sure, but I never thought it was so complicated.

View on HN

I agree, that's always been the most likely explanation to me as well. You can see this phenomena with many things...

I was at a concert and saw loudspeakers on the top of some poles. I immediately associated them with shelf speakers, and my brain told me they couldn't be more than a foot tall. Then later I saw a worker climbing the pole to do maintenance and realized each speaker box was taller than he was.

I've also noticed this illusion in the city. There's a particular street that has a hill. As you drive up this hill, the top of a skyscraper is framed by the road and trees nearby, and it looks absolutely massive. Then you crest the hill and see the entire thing (along with the rest of the buildings downtown) and they look so much smaller and distant. It's really striking.

But that's complicated enough! Our brains use ad-hoc algorithms even for simple things like relative size. Look at relative brightness - there are endless optical illusions where a patch of dark and a patch of light are actually exactly the same tone.

Context is everything to our brains/vision system. Its alarming how warped our perception is.

It would be alarming if our perception was not warped—contextual awareness is far more useful than absolute perception in non-specialized situations (like most survival tasks).

Reply on news.ycombinator.com