La ilusión lunar

Pocas personas estarán en desacuerdo si decimos que la luna muestra el máximo de su esplendor y encanto cuando está cerca del horizonte y parece estar más cerca y ser más grande que cuando se encuentra en lo alto del firmamento. Pero esto es una ilusión, la "ilusión lunar" para ser precisos: la distancia recorrida por la luz reflejada desde la luna al ojo del observador es esencialmente la misma, no importando cuál sea la elevación de la luna. Observamos una ilusión similar cuando el sol se pone y también con respecto a las distancias celestiales entre estrellas a diferentes elevaciones.

Pero la contemplación de la ilusión lunar no sólo nos cautiva: también es quizás el más antiguo problema científico sin resolver. Se pueden encontrar referencias a ella en las tablillas de arcilla de la librería real de Nínive y Babilonia, que datan de antes del siglo sexto A.C., así como en una serie de leyendas chinas atribuidas a Lieh Tzu, cuyo origen se remonta al siglo quinto A.C. Muchos de los más importantes científicos y matemáticos de la historia han analizado el fenómeno: da Vinci, Kepler, Descartes, por nombrar a unos pocos.

Durante la mayor parte de la historia escrita, se pensó que la ilusión era una consecuencia de procesos físicos. Por ejemplo, Aristóteles, en el siglo tres A.C., y Tolomeo, en el siglo dos A.C., atribuyeron erróneamente la ilusión a las propiedades ópticas de la atmósfera, que harían que los objetos se vieran de mayor tamaño. Alhazen (Ibn al-Haytham) relacionó la ilusión con la apariencia aplastada del domo del cielo.

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