Kepler published the Mysterium Cosmographicum in the spring of 1597. Although the idea behind the book was entirely wrong, Kepler always looked back on it as his most important work, as it was the cause of everything that followed. The rest of his career would be spent on trying to revise and improve this theory. All of Kepler's important contributions stemmed from this one incorrect idea – an idea that Kepler valued far above anything else he'd done.

When it came on the scene, however, the Mysterium failed to make much of a splash. Kepler was an unknown astronomer, and his wildly enthusiastic ramblings failed to capture the interest of the scholarly elite. The book was read, but rarely understood. Scientists who considered themselves a part of the modern scientific era disdained it, because they were determined to leave such mysticism behind. They overlooked its revolutionary scientific potential. On the other hand, scientists of the old era thought Kepler's book was wonderful, mainly because they had latched onto the religious and mystical portions. They failed to see the book's scientific potential. Few people were able to see the work for what it really was, a radically modern scientific work covered by the trappings of the old era. Fortunately for Kepler, at least one astronomer did read and understand the promise of the Mysterium: Tycho de Brahe.

Born in 1546, Tycho de Brahe was one of the seventeenth century's top astronomers. Wealthy and arrogant, he had once entered into a duel over who was the best mathematician and had a piece of his nose sliced off. Undaunted, Brahe had a new nose made from gold and silver and wore it proudly. For much of his professional life, he lived in Denmark, on the island of Hveen. The ruler of Denmark so valued Tycho that he had given Tycho the entire island, where Tycho ruled like a feudal master. He built a grand observatory called Uraniburg, in which he kept a collection of the era's best observational equipment.

Tycho was obsessed with making observations, an unpopular pursuit at the time. Observing the stars wasn't considered a necessary element of astronomy. The telescope had yet to be invented, and many astronomers were content to use data that had been collected over the preceding centuries. Even Copernicus, in his revolutionary work, included fewer than thirty new observations. Tycho was ahead of his time in recognizing the importance of accurate and current data.

Kepler was also unusually concerned with accuracy, and needed more data to revise his system of the universe – he knew that only Tycho could provide it. But unfortunately, Tycho lived in Denmark. Even if Tycho had invited Kepler to join him, the younger astronomer had no funds to make the long and arduous journey.

Kepler knew that someday he would need to find a way to get to Tycho, and get his hands on Tycho's observations, but for the moment, he bided his time. From 1597 to 1599, Kepler stayed in Gratz, studying mathematics and busying himself with a number of minor astronomical investigations.

Kepler also turned his attention toward his personal life, as his friends had decided it was time for him to take a wife. After a complicated yearlong courtship, Kepler married Barbara Muehleck, a 23-year-old widow. Kepler and Muehleck were set up by a mutual friend. Kepler seems to have had little early affection for his new wife, noting that she was "simple of mind and fat of body." None of his later writings contradicted this early view – Kepler believed her to be stupid, cranky, temperamental, and greedy. Nevertheless, they stayed together for fourteen years, having four children.

In 1598, life in Gratz got distinctly less pleasant for Kepler, when the Catholic Archduke Ferdinand of Hapsburg decided to rid Austria of as many Protestants as possible. In the summer of 1598, the Protestant school where Kepler taught was closed down. Then, in September, the town of Gratz exiled all the Protestant preachers and teachers – including Kepler. Thanks to the help of a friend in the Jesuit order, a very pro-science Catholic sect, Kepler was allowed to return home in only a month. But Kepler was now unhappier than ever. He wrote again to his old teacher Maestlin, begging the older man to help Kepler find a job in his native land. Maestlin was either unable or unwilling to help, and Kepler was forced to remain where he was.

In 1599, Tycho got into a fight with the new King of Denmark, and fled the country for Prague. The Emperor Rudolph II appointed Tycho to be the Imperial Mathematicus – head mathematician and astronomer, and gave him a castle in the town of Benatek. Prague was much closer to Gratz than Denmark had been, and the journey seemed much more bearable to Kepler now that he was so desperate to leave. On January one, 1600, Kepler began the new century by setting off for Prague.