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The Telescope. The invention of the telescope enabled Europeans to inaugurate a new age in astronomy. Shown here is Johannes Hevelius, an eminent German-Polish astrologer (1611– 1697), making an observation with his telescope. Hevelius’s observations were highly regarded. He located his telescope on the roof of his own house, and by the 1660s, his celestial observatory was considered one of the best in Europe.

© Bibliothèque Nationale, Paris/SuperStock

Galileo’s revelations, published in The Starry Messenger in 1610, stunned his contemporaries and probably did more to make Europeans aware of the new picture of the universe than the mathematical theories of Copernicus and Kepler did. The English ambassador in Venice wrote to the chief minister of King James I in 1610:

I send herewith unto His Majesty the strangest piece of news … that he has ever yet received from any part of the world; which is the annexed book of the Mathematical Professor at Padua [Galileo], who by the help of an optical instrument … has discovered four new planets rolling about the sphere of Jupiter… . So upon the whole subject he has first overthrown all former astronomy… . By the next ship your Lordship shall receive from me one of the above instruments [a telescope], as it is bettered by this man.7

During a trip to Rome, Galileo was received by scholars as a conquering hero. Grand Duke Cosimo II of Florence offered him a new position as his court mathematician, which Galileo readily accepted. But even in the midst of his newfound acclaim, Galileo found himself increasingly suspect by the authorities of the Catholic Church.

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Kepler and the Emerging Scientific Community

The exchange of letters between intellectuals was an important avenue for scientific communication. After receiving a copy of Johannes Kepler’s first major work, the Italian Galileo Galilei wrote to Kepler, inaugurating a correspondence between them. This selection contains samples of their letters to each other.

Galileo to Kepler, Padua, August 4, 1597

Your book, highly learned gentleman, which you sent me through Paulus Amberger, reached me not days ago but only a few hours ago, and as this Paulus just informed me of his return to Germany, I should think myself indeed ungrateful if I should not express to you my thanks by this letter. I thank you especially for having deemed me worthy of such a proof of your friendship… . So far I have read only the introduction, but have learned from it in some measure your intentions and congratulate myself on the good fortune of having found such a man as a companion in the exploration of truth. For it is deplorable that there are so few who seek the truth and do not pursue a wrong method of philosophizing. But this is not the place to mourn about the misery of our century but to rejoice with you about such beautiful ideas proving the truth… . I would certainly dare to approach the public with my ways of thinking if there were more people of your mind. As this is not the case, I shall refrain from doing so… . I shall always be at your service. Farewell, and do not neglect to give me further good news of yourself.

Yours in sincere friendship,

Galilaeus Galilaeus

Mathematician at the Academy of Padua

Kepler to Galileo, Graz, October 13, 1597

I received your letter of August 4 on September 1. It was a double pleasure to me. First because I became friends with you, the Italian, and second because of the agreement in which we find ourselves concerning Copernican cosmography. As you invite me kindly at the end of your letter to enter into correspondence with you, and I myself feel greatly tempted to do so, I will not let pass the occasion of sending you a letter with the present young nobleman. For I am sure, if your time has allowed it, you have meanwhile obtained a closer knowledge of my book. And so a great desire has taken hold of me, to learn your judgment. For this is my way, to urge all those to whom I have written to express their candid opinion. Believe me, the sharpest criticism of one single understanding