The "Mountain Or Valley?" Illusion

Thanks to Skillshare for supporting this video: http://skl.sh/MinutePhysics for 2 free months! This video is about a multistable perceptual illusion, similar to the hollow face illusion, whereby maps or aerial or satellite photos look upside down/inside out, ie, concave (valley) parts look convex and convex (mountainous) parts look concave. Just flip the images around and things will make a lot more sense! It s just because our eyes gauge depth based on the location of shadows, and the sun always casts shadows on the bottoms of things. Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics And Google+ (does anyone use this any more?) - http://bit.ly/qzEwc6 REFERENCES Twitter posts: https://twitter.com/Astro2fish/status/859799730565414912 https://twitter.com/BadAstronomer/status/859800278358528001 Bad Astronomy Blog post: http://blogs.discovermagazine.com/badastronomy/2010/05/19/a-lunar-illusion-youll-flip-over/ Multistable perception http://en.m.wikipedia.org/wiki/Multistable_perception Top-left Lighting http://en.m.wikipedia.org/wiki/Top-left_lighting Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich