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You can't believe your eyes! Honest.

Take a look at this Astronomy Picture of the Day and see if you don't agree. Then come back and read the comments that follow.

The first thing that came to mind after I absorbed the shock of this illusion is that this probably ties to the ongoing debate over the color of stars - especially the perceived color of double stars. (Excellent observers frequently have very different perceptions.) But if you;re still doubting your eyes, read the comments of my friend Don Foster. Don is an engineer and professor with lots of experience in optics and color. Here's what he had to say.

Fascinating! Of course, it would be more accurate to ask "Are these the same brightness?" rather than "Are these the same color?" To use the word "color" implies a hue rather than a degree of gray, and these squares are neutral, not tinted. So, strictly speaking, they're the same color because they have the same proportions of red, green, and blue (which would be true even if one square WAS darker than the other).

Anyway, I was absolutely convinced that square B was lighter than square A. So I saved the image and measured the red, green, and blue values of both squares -- 120, 120, 120 and 120, 120, 120.

This must be a Bush Administration trick.
Posted by Greg Stone at July 17, 2007 08:11 AM Comments? Please email me: gstone@umassd.edu

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