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.

2023 December 18
A checkerboard is shown with squares colored light and dark grey.
A green tube sits on the board and casts a shadow. The image has a 
letter A typed on a dark square, and a letter B types on a light square
cast in shadow. The question is asked if the two squares, A and B, are 
really the same color.
Please see the explanation for more detailed information.

The Same Color Illusion
Image Credit: Edward H. Adelson, Wikipedia

Explanation: Are squares A and B the same color? They are! To verify this, either run your cursor over the image or click here to see them connected. The featured illusion, an example of the same color illusion, illustrates that purely human perceptions in science may be ambiguous or inaccurate, even such a seemingly direct perception as relative color. 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.

APOD Year in Review (2023): RJN's Night Sky Network Lecture
Tomorrow's picture: california on high

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