Epitome of Copernican AstronomyJohannes Kepler

Kepler's most systematic presentation of heliocentric astronomy, published in three parts between 1617 and 1621. Cast as a textbook in question-and-answer form, the Epitome gathers the results of the Astronomia Nova and the Harmonice Mundi into a single account of the heavens governed by the three laws now bearing Kepler's name: planets move in ellipses with the sun at one focus; the line from sun to planet sweeps equal areas in equal times; the square of the period is proportional to the cube of the mean distance.

The work does more than tabulate laws. Kepler argues that the motion of the planets must have a physical cause, a vis motrix radiating from the sun, and he ties the structure of the solar system to his convictions about geometrical harmony. He extends the new astronomy beyond the six known planets to the moons of Jupiter and to the moon itself, treating all orbital motion by a single mathematical pattern.

Placed on the Roman Index soon after publication, the Epitome nonetheless became the standard reference work for Copernican astronomy across seventeenth-century Europe. Newton read it. The Principia would later supply the physical cause Kepler had sought, deriving his three laws from universal gravitation, but the laws themselves had been stated, with full generality, in this book.