Johannes Kepler was born on December 27, 1571, in the small German town of Weil- der-Stadt. He was born at the tail end of the European Renaissance, an age of intellectual, religious, cultural, and scientific transformation. But Kepler's own early childhood showed no such signs of enlightenment. The young Kepler was trapped in his own period of personal depression and darkness. The Kepler family tree had distinguished roots – his arrogant grandfather Sebaldus Kepler had even served as town mayor. But by the time Kepler came on the scene, the family had fallen into a state of disrepair, filled with tormented personalities, hot tempers, invalids, and criminals.
Sebaldus and his wife, Katherine Mueller, had twelve children. Heinrich, Kepler's father, was the oldest surviving child; three others had died in infancy. When he was twenty-four years old, Heinrich married Katherine Guldenmann – Johannes was their first child. Katherine had a slightly less auspicious pedigree than Heinrich. She was an innkeeper's daughter whose aunt had been accused of being a witch and had been burned at the stake.
Heinrich was a restless husband who abandoned his family often. When Kepler was only three, Heinrich left to fight the Protestant armies in the Netherlands. This was a public embarrassment for the Keplers – one of many that Heinrich would cause – since the Kepler family itself was solidly Protestant. Heinrich came and left frequently through Kepler's youth. At one point, he was accused of a crime and almost hanged. After briefly running a tavern, the itinerant Heinrich abandoned the family for good in 1588.
Johannes Kepler had six brothers and sisters, three of whom died in childhood. Of the remaining three, two grew up to be normal, law-abiding citizens. The last one, Heinrich, was an epileptic who was always either sick or in trouble. He eventually ran away from home after Heinrich Sr. threatened to sell him.
Historians have an incredibly detailed sketch of Kepler's childhood, thanks, in large part, to the scientist himself. At the age of twenty-six, Kepler drafted a horoscope of his entire family. He also spent a fair amount of time analyzing his own personality. Kepler recorded everything, including the time of his conception (May 16, 1571), the length of his mother's pregnancy (224 days, nine hours, and fifty-three minutes), and his own opinions of each member of his family.
The image we are left with is not a pretty one. Grandfather Sebaldus was "remarkably arrogantshort tempered and obstinate" and Grandmother Katherine was "restless, clever, and lyingan inveterate troublemaker, extreme in her hatred, a bearer of grudges" Mother Katherine is described as "small, thin, swarthy, gossiping, and quarrelsome." But it is Kepler's father who bears the brunt of Kepler's familial criticisms. In Kepler's autobiographical study, Heinrich appears as a man "vicious, inflexible, quarrelsome, and doomed to a bad end."