L'illusion de la Lune

Tout le monde s'accorde à dire que la Lune est plus merveilleuse et plus magnifique lorsqu'elle s'approche de l'horizon, apparaissant plus proche et plus grosse que lorsqu'elle est haute dans le ciel. Mais il s'agit d'une illusion, " l'illusion de la Lune ", pour être précis : la distance parcourue par la lumière réfléchie de la lune vers l'oeil d'un observateur est essentiellement la même, indépendamment de l'élévation de la Lune. Une illusion similaire est observée pour le soleil couchant et les distances célestes entre les points neutres à des élévations différentes.

Mais l'illusion de la Lune est non seulement un spectacle captivant, mais elle constitue également sans doute le plus ancien problème scientifique non résolu. Elle est mentionnée sur les tablettes en argile de la bibliothèque royale de Nineveh et de Babylone, qui datent d'avant le sixième siècle avant JC, ainsi dans un recueil de légendes chinoises attribuées à Lieh Tzu datant du cinquième siècle avant JC. Un grand nombre des principaux scientifiques et mathématiciens de l'Histoire ont analysé le phénomène : de Vinci, Kepler, Descartes, pour n'en citer que quelques-uns.

Pendant la majeure partie de la période couverte par les écrits historiques, l'illusion était considérée comme une conséquence des processus physiques. Par exemple, Aristote au troisième siècle avant JC et Ptolémée au deuxième siècle après JC ont attribué à tort l'illusion aux propriétés grossissantes de l'atmosphère. Alhazen (Ibn al-Haytham) a lié l'illusion à l'aspect aplati de la voûte du ciel.

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