The astronomer Christen Sørensen Longomontanus, engaged by Tycho in 1589 as his assistant in his great astronomical observatory of Uraniborg, had rendered invaluable service for eight years.

Having left the island of Hven with his master, he had obtained his discharge at Copenhagen on June 1, 1597, in order to study at some German universities.

He had rejoined Tycho at Prague in January 1600, bringing the rest of Tycho's astronomical instruments with him.

Having completed the Tychonic lunar theory, he turns homeward again in August.