Tycho Brahe · 1588
Read the translation (PDF) · Editorial footnotes (PDF)
When a brilliant comet blazed across Europe in 1577, the finest instruments of the age were turned upon it, and the measurements shattered the ancient belief in unchanging, perfect heavens: the comet moved freely where solid crystalline spheres were supposed to be.
The first part follows the comet night by night from November 1577 into January 1578 — a running observational log giving its position, the direction of its tail, and its changing brightness.
To fix the comet’s positions Brahe had first to fix the stars, and the second chapter works through the reference stars one at a time: the bright star of the Lyre, the shoulders of Aquarius, the mouth and wing and knee and breast of Pegasus, Scheat, the bright star of the falling eagle. Each is given a measured longitude and latitude, tabulated against both the Alphonsine and the Copernican computations so the reader can see where the older tables fail. An addition by the author, drawn from later years and better instruments, revises the figures again.
From measurement the book turns to argument. The comet showed no measurable parallax, placing it far beyond the Moon — in the aethereal region where, on Aristotelian physics, nothing new could be generated and nothing solid could be crossed. The later chapters draw the consequence and set out Brahe’s own arrangement of the cosmos: the Earth at rest at the centre, the Sun circling the Earth, and the remaining planets circling the Sun.
The dispute Brahe entered was old — whether comets are sublunary weather or celestial objects — and he settled it with numbers rather than authority. If the comet passed through the spheres, the spheres were not there. That inference did more damage to the inherited cosmos than any argument from Copernicus, and it did so on ground the Aristotelians had chosen themselves.
The work is of 1588, but the translated source is the later Frankfurt printing issued from the house of Gottfried Tampach, begun at Uraniborg and completed at Prague. It carries a dedication to the imperial councillor Johannes Barvitius written not by Brahe but by his son-in-law, who saw the volume through the press after Brahe’s death.