The Works of Galileo

Starry Messenger (1610)

Observing lunar topography

With a multitude of diagrams Galileo taught us how to observe the lunar surface. What appears as an isolated peak one night, may become a chain of mountains the next night, or converge in a circular structure after that. He was not mapping the moon, or implying that a crater of gigantic size is present in the bottom center of the lunar face, but proving how to observe the Moon’s topography, contrary to the Aristotelians. (Figure 1) (Figure 2) (Figure 3) (Figure 4)

“When the Moon displays herself to us with brilliant horns, the boundary dividing the bright from the dark part does not form a uniformly oval line, as would happen in a perfectly shaped spherical solid, but is marked by an uneven, rough, and very sinuous line, as the figure shows.... what causes even greater wonder is that very many bright points appear within the dark part of the Moon... gradually these are increased in size and brightness [and...] joined with the rest of the bright part.... Now, on Earth, before sunrise, aren’t the peaks of the highest mountains illuminated by the Sun’s rays while shadows still cover the plain?” Galileo, Sidereus Nuncius, trans. Albert Van Helden (University of Chicago, 1989).

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Galileo, 1610. 9v.

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Figure 2 Figure 2 - Return to Text

Galileo, 1610. 10r.

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Figure 3 Figure 3 - Return to Text

Galileo, 1610. 10v.

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Figure 4 Figure 4 - Return to Text

Galileo, 1610. C2v-C3r.

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Exhibit credit: Kerry Magruder, with the assistance of , Marilyn B. Ogilvie, Duane H. D. Roller.

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