The Works of Galileo

Foundations of Mathematical Physics

Astronomy: Regiomontanus, Kalendarium

In another work, the Kalendarium (Figure 1) , Regiomontanus used his updated Earth-centered models to predict the positions of the Sun and Moon for 40 years (Figure 2) . These positions provided the foundation for calculations of lunar and solar eclipses (Figure 3) . Columbus had a copy of a German edition of this work with him on his fourth voyage, when he used the prediction of this 1504 lunar eclipse to frighten his Jamaican hosts. Suitably updated, an observer-centered system can still serve today to accurately position the Sun, Moon and planets, as in a planetarium’s mechanical-optical star projector. Each gear in a mechanical-optical star projector corresponds to the geometrical devices used in Earth-centered astronomical systems (Figure 4) .

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Regiomontanus, Kalendarium (1476). Title page.

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Regiomontanus, Kalendarium (1476). Positions of Sun and Moon.

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Regiomontanus, Kalendarium (1476). Lunar eclipse prediction.

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Goto Optical GS planetarium projector (observer-centered).

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

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