Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2007 July 17
See Explanation.  Clicking on the picture will download
 the highest resolution version available.

The Same Colour Illusion
Credit: Edward H. Adelson, Wikipedia

Explanation: Are square A and B the same colour? They are. Are too. To verify this, click on the above image to see them connected. The above illusion, called the same colour illusion, illustrates that purely human observations in science may be ambiguous or inaccurate. Even such a seemingly direct perception as relative colour. Similar illusions exist on the sky, such as the size of the Moon near the horizon, or the apparent shapes of astronomical objects. The advent of automated, reproducible, measuring devices such as CCDs have made science in general and astronomy in particular less prone to, but not free of, human-biased illusions.

Tomorrow's picture: lakeside planets

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