large observatory in Christian Europe. Marriage to Kirsten Jørgensdatter Towards the end of 1571, Tycho fell in love with Kirsten, daughter of Jørgen Hansen, the Lutheran minister in Knudstrup. As she was a commoner, Tycho never formally married her, since if he did he would lose his noble privileges. However, Danish law permitted morganatic marriage, which meant that a nobleman and a common woman could live together openly as husband and wife for three years, and their alliance then became a legally binding marriage. However, each would maintain their social status, and any children they had together would be considered commoners, with no rights to titles, landholdings, coat of arms, or even their father's noble name. While King Frederick respected Tycho's choice of wife, himself having been unable to marry the woman he loved, many of Tycho's family members disagreed, and many churchmen would continue to hold the lack of a divinely sanctioned marriage against him. Kirsten Jørgensdatter gave birth to their first daughter, Kirstine (named after Tycho's late sister) on 12October 1573. Kirstine died from the plague in 1576, and Tycho wrote a heartfelt elegy for her tombstone. In 1574, they moved to Copenhagen where their daughter Magdalene was born, and later the family followed him into exile. Kirsten and Tycho lived together for almost thirty years until Tycho's death. Together, they had eight children, six of whom lived to adulthood. 1572 supernova On 11 November 1572, Tycho observed (from Herrevad Abbey) a very bright star, now numbered SN 1572, which had unexpectedly appeared in the constellation Cassiopeia. Because it had been maintained since antiquity that the world beyond the Moon's orbit was eternally unchangeable (celestial immutability was a fundamental axiom of the Aristotelian world-view), other observers held that the phenomenon was something in the terrestrial sphere below the Moon. However, Tycho observed that the object showed no daily parallax against the background of the fixed stars. This implied that it was at least farther away than the Moon and those planets that do show such parallax. He also found that the object did not change its position relative to the fixed stars over several months, as all planets did in their periodic orbital motions, even the outer planets, for which no daily parallax was detectable. This suggested that it was not even a planet, but a fixed star in the stellar sphere beyond all the planets. In 1573,