Epitome Astronomiae Copernicanae

What it is

The Epitome Astronomiae Copernicanae is an astronomy textbook by Johannes Kepler, published in three parts between 1618 and 1621, written in a question-and-answer format across seven books.

Why it matters

It contained the first printed version of Kepler's third law of planetary motion and extended his elliptical model to all the planets. Kepler also argued, using telescope observations of Jupiter's moons made by Simon Marius, that the same physical laws governed moons orbiting planets as governed planets orbiting the Sun. Because it defended heliocentrism so clearly, the Catholic Church placed the first volume on its Index of Forbidden Books in 1619, showing how dangerous this science could be seen at the time.

Look closer

• Why might a textbook, meant to teach rather than to argue originally, have been seen as dangerous enough to ban?
• What does it mean that Kepler used another astronomer's telescope observations to support his own laws?
• Why do you think Kepler chose a question-and-answer format for this book?