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Meridian Lines

Meridian at The Cathedral of Milan

Giesen presents the yearly analemma for the transit hour at the Basilica of Milan, where the sunlight starts nearly 24 meters above the floor.  Giesen illustrates how the sun shines through a small hole in the southern wall to cast light on the meridian line each day, and shows the shape of the sun's disk on the Basilica's floor.  Included are a nice set of equations to compute the sun's image size and shape on the floor.  Giesen also shows the change in the earth's obliquity over the centuries has changed the position of the sun's position at summer and winter solstice.


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