Abstract
PROF. E. G. BORING and his associates at the Harvard Psychological Laboratory have quite recently undertaken precise measurements to determine how large the moon appears, both on the horizon and near the zenith (Sky and Telescope, Sept.). Various observers compared the moon with an artificial moon placed at a standard distance, and the size of the artificial moon could be varied to agree with the real moon. An arrangement was made to control the orientation of the observer's head, so that the angle between direct vision and the elevation of the moon could be measured. The artificial moon, placed at a distance of 12 ft., appeared from 2° to 6° in diameter to people with normal vision and using both eyes. The experiments were conducted to choose between four modern theories which are associated with the physiology of the eye. The old theory that the moon is contrasted with terrestrial objects when near the horizon is ruled out by the fact that this illusion disappears when we view the horizon moon with the head upside down. The theory that the celestial sphere looks flattened overhead, the apparent distance of the moon thus varying, is also eliminated. Ames's theory alone out of the four modern theories is not finally rejected. When the eyes are raised, it has been found that the right eye tends to rotate clockwise, as viewed from the back, with respect to the left eye, and this fact may explain the moon illusion for binocular vision. It is admitted, however, that the results are not conclusive.
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Illusions about the Size of the Moon. Nature 150, 629 (1942). https://doi.org/10.1038/150629b0
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DOI: https://doi.org/10.1038/150629b0