Free Galileo's Daughter by Dava Sobel Page A

Copernicus made more sense of the passage than either Aristotle or Ptolemy, as Galileo spent almost half of this letter explaining.
On this day, when the Lord delivered up the Amorrites to the Israelites, Joshua prayed to the Lord, and said in the presence of Israel: Stand still, o sun at Gabhaon, o moon, in the valley of Aialon! And the sun stood still, and the moon stayed, while the nation took vengeance on its foe. Is this not recorded in the Book of Hashar? The sun halted in the middle of the sky; not for a whole day did it resume its swift course. Never before or since was there a day like this, when the Lord obeyed the voice of a man; for the Lord fought for Israel. [Josh. 10:12-14]
    The Ptolemaic system granted the Sun two motions. One of these, a slow annual progression from west to east, belonged strictly to the Sun itself. The other, more apparent, motion of the Sun across the sky over the course of the day—most probably the motion Joshua had sought to halt—actually belonged to the Ptolemaic Primum Mobile, the sphere of the highest sky, which spun all the other spheres containing Sun, Moon, planets, and stars around the Earth every twenty-four hours. God’s stopping only the Sun would not have achieved Joshua’s desire. On the contrary, it would have made night arrive about four minutes early.
    As Copernicus viewed the sky, however, the passage of day to night resulted from the turning of the Earth. Galileo agreed with Copernicus that the Earth somehow drew this motion from the Sun. Galileo had further observed the Sun to have its own monthly rotation, which he discovered during his studies of sunspots. Just as the light of the Sun illuminated all the planets, so too its motion energized them to pursue their orbits. Therefore, if God had stopped the Sun’s rotation, the Earth would have stopped, too, and the day stretched out to accommodate Joshua’s needs.
    Later Galileo would point out that when the Sun stood still in the biblical account, it did so “in the middle of the sky”—precisely where the Copernican system placed it. This reference to location could not be taken to mean the Sun had been standing in the high noontime position, for then Joshua would have found time enough to fight his battle without praying for a miracle to prolong the day.
    Despite the strength of his argument, Galileo personally wished to abandon all such astronomical interpretations, on the grounds that the Bible spoke to a more important purpose. As he had once heard the late Vatican librarian Cesare Cardinal Baronio remark, the Bible was a book about how one goes to Heaven—not how Heaven goes.
    “I believe that the intention of Holy Writ was to persuade men of the truths necessary for salvation,” Galileo continued his letter to Castelli, “such as neither science nor any other means could render credible, but only the voice of the Holy Spirit. But I do not think it necessary to believe that the same God who gave us our senses, our speech, our intellect, would have put aside the use of these, to teach us instead such things as with their help we could find out for ourselves, particularly in the case of these sciences of which there is not the smallest mention in the Scriptures; and, above all, in astronomy, of which so little notice is taken that the names of none of the planets are mentioned. Surely if the intention of the sacred scribes had been to teach the people astronomy, they would not have passed over the subject so completely.”
    Castelli shared this exquisite exposition with friends and colleagues, who hand-copied it and forwarded it numerous times. Galileo now returned to predicting the positions of the Medicean satellites and to penning responses to various published attacks against his own published works. When his health faltered in March, Castelli, who had been begging Galileo to take better care of himself, stepped in to help him.
    In the early days of summer, at the Convent of San Matteo in Arcetri,