Francesco Bianchini

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For Giovanni Bianchini (1410-ca. 1449), see Giovanni Bianchini.

Francesco Bianchini (December 13, 1662March 2, 1729) was an Italian philosopher and scientist. He worked for the curia of many popes, including being secretary of the commission for the reform of the calendar, working on the method to calculate the correct date for Easter in a given year.

A gnomon in the south wall of the Santa Maria degli Angeli e dei Martiri projects the sun's image onto Bianchini's line every solar noon
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A gnomon in the south wall of the Santa Maria degli Angeli e dei Martiri projects the sun's image onto Bianchini's line every solar noon

He published many books, including A Universal History, and Hesperi et Phosphori nova Phaenomena in which he deduced a rotational period from the observation of the surface of Venus. Today, we know that this is impossible, because of the thick cloud cover on this planet. He also worked on the parallax of Venus, and he measured the precession of the Earth's rotational axis.

As part of his efforts to improve the accuracy of the calendar, Bianchini constructed several important meridian lines, devices for calculating the position of the sun and stars. The most notable of these are in the cathedral church of San Petronio in Bologna, and in the basilica of Santa Maria degli Angeli e dei Martiri in Rome.

His point of view on the Copernican system is not evident, but it was noted that the picture of the planetary system in his book about Venus has an empty center.

Craters on Mars and the Moon were named in his honor.