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The Oxford Compendium of Visual Illusions$
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Arthur G. Shapiro and Dejan Todorovic

Print publication date: 2017

Print ISBN-13: 9780199794607

Published to Oxford Scholarship Online: June 2017

DOI: 10.1093/acprof:oso/9780199794607.001.0001

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PRINTED FROM OXFORD SCHOLARSHIP ONLINE (oxford.universitypressscholarship.com). (c) Copyright Oxford University Press, 2021. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in OSO for personal use. date: 28 September 2021

The New Moon Illusion

The New Moon Illusion

(p.283) Chapter 31 The New Moon Illusion
The Oxford Compendium of Visual Illusions

Brian Rogers

Stuart Anstis

Oxford University Press

When the sun is near the horizon and the moon is visible and higher in the sky, there is a compelling illusion that the sun is not in a direction perpendicular to the boundary between the lit and dark sides of the moon. This New Moon illusion has been observed and discussed previously but without a complete explanation. This chapter argues that both perceptual and cognitive factors contribute to the illusion and that it arises from the fact that the straight line joining the sun and the moon describes a great circle over the flattened dome of the sky. The New Moon illusion also raises the question of how we are able to judge the straightness of extended straight and parallel lines.

Keywords:   illusion, moon illusion, New Moon illusion, cognitive factors, lines

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