Treasures of the Bodleian

More than any earlier astronomer, Tycho registered his results systematically, using instruments built to unprecedented specifications. He presented this lavish, hand-coloured copy of his book of astronomical instruments to Grimani, the Doge of Venice, in 1599, as a kind of curriculum vitae. One of the engravings displayed here shows Tycho in his observatory, next to a large quadrant of his own design. The key printed opposite states: ‘The use of the large quadrant is for determining the altitudes of the stars within one-sixth of a minute, by sighting through the upper and lower slits of one of the pinnules and along the two corresponding sides of the cylinder, and reading off the altitude on the outer rim of the quadrant in accordance with the position of this pinnule.’

The triangular astronomical sextant pictured here determines distances between two stars. Brahe used this (and the many other large instruments he designed) to make systematic and accurate observations over nearly forty years. He guarded his data fiercely, knowing that it would provide material to confirm or refute existing theories, but died before he was able to make the analysis. His family allowed full access to his assistant Johannes Kepler, who used it to formulate the Rudolphine Tables and laws of planetary motion.