The first part of the book was mostly about Tycho Brahe. I won't add much to the one-sentence (if that much) that he gets in science courses, namely "he made very accurate observations of the movement of the planets, which were useful in overthrowing the geocentric view of the solar system," or something like that. I will say that Ferguson makes clear that these accurate observations were obtained purposefully, and that Brahe had to develop his own astronomical instruments in order to get them. She also discusses the difficulty of getting along with Brahe, who became, at least in his own mind, an astronomer equal in status to the rulers of his day. Kepler eventually became an employee, or associate, of Brahe's. (Kepler, unlike Brahe, was not born to a fortune, and his status, and where his support was coming from, were often unclear.)
Ferguson indicates clearly that Kepler's view of the solar system, and the universe at large, as a divinely ordered system, which was there to be understood, became the driving force behind his life's work. The one-phrase summary of Kepler's work is something like "he developed three laws of planetary motion." That is true, as far as it goes, and that alone would have been enough to assure him of scientific immortality, but Kepler did more.
Kepler has been called, with justification, "the world's first astro-physicist."
His story, Somnium, has been called the first work of science fiction ever written.
The Wikipedia article on Kepler, and Ferguson, agree that he was a pioneer in the science of optics, introducing the use of diagrams of light rays. Ferguson (292) also says that he discovered that the image on the retina is upside down and backwards. He was the first to believe that the intensity of light varies inversely as the square of the distance from the source.
Ferguson says that he was probably the first to incorporate logarithms into his astronomical tables. He almost discovered that gravity was a force. He didn't get so far as applying the inverse square relationship to gravity, as Newton came to do.
When Kepler was dying, a pastor asked him the basis of his hope for salvation. He responded, "Solely on the merit of our Savior Jesus Christ, in whom is found all refuge, solace, and salvation." (p. 356 of Ferguson)
He wrote his own epitaph, which said:
In his most important book, he included this prayer:
It now remains that at last, with my eyes and hands removed from the tablet of demonstrations and lifted up towards the heavens, I should pray, devout and supplicating, to the Father of lights: O Thou Who dost by the light of nature promote in us the desire for the light of grace, that by its means Thou mayest transport us into the light of glory, I give thanks to Thee, O Lord Creator, Who hast delighted me with Thy makings and in the works of Thy hands have I exulted. Behold! now, I have completed the work of my profession, having employed as much power of mind as Thou didst give to me; to the men who are going to read those demonstrations I have made manifest the glory of Thy works, as much of its infinity as the narrows of my intellect could apprehend. My mind has been given over to philosophizing most correctly: if there is anything unworthy of Thy designs brought forth by me—a worm born and nourished in a wallowing place of sins—breathe into me also that which Thou dost wish men to know, that I may make the correction: If I have been allured into rashness by the wonderful beauty of Thy works, or if I have loved my own glory among men, while I am advancing in the work destined for Thy glory, be gentle and merciful and pardon me; and finally deign graciously to effect that these demonstrations give way to Thy glory and the salvation of souls and nowhere be an obstacle to that. Same prayer as above, from Harmonies of the World, by Johannes Kepler, tr. Charles Glenn Wallis , at sacred-texts.com, which, as best I can determine, is copyright-free. The emphasis is in the original.This is from the end of the ninth section, or chapter, of Kepler's book.
Thanks for reading. Especially if you are a scientist, pray Kepler's prayer.