Tycho's 1572 'new star' proved the heavens could change

On November 11, 1572, Danish astronomer Tycho Brahe spotted a brilliant new star in Cassiopeia, and his measurements showed it lay out among the distant stars, proving that the supposedly unchanging heavens could change. It outshone Venus, could be seen in daylight and stayed visible to the naked eye for about 18 months.

Tradition held that the sphere of the stars had not changed since creation, so a newcomer was assumed to sit in the atmosphere or among the planets. If so, it should drift against the background stars as the Moon and planets do. Michael Maestlin in Tübingen and Thomas Digges in England lined it up with fixed stars using stretched threads and saw no shift.

Tycho went further. He had just built a sextant with arms 5.5 feet long and drew up a table to correct its small errors. With it, he confirmed the star did not move against its neighbors: it belonged to the realm of the stars itself.

His 1573 book, De nova stella, made him famous across Europe and caught the attention of the king of Denmark, who gave him the island of Ven and funded the Uraniborg observatory, where Tycho spent two decades measuring star and planet positions with unprecedented precision, years before the telescope.

The “new star” was really a dying one. The explosion, catalogued as SN 1572, left a remnant about 13,000 light-years away: the wreck of an exploded white dwarf. In 2008, astronomers captured light from the 1572 blast that had bounced off interstellar dust and was only now reaching Earth, more than four centuries after the direct light swept past. Its spectrum showed that Tycho’s star belonged to the majority class of normal Type Ia supernovae, the thermonuclear explosions of white dwarfs.