Cassiopeia's five bright stars form the sky's most recognisable W, but the constellation's most consequential contribution to astronomy was a star that appeared where no star had been seen before, and then vanished again within a couple of years.
In November 1572, the Danish astronomer Tycho Brahe observed a new point of light in Cassiopeia bright enough to be seen in daylight, brighter for a time than Venus, where his own careful star charts showed nothing at all. Tycho measured its position repeatedly over months and could detect no parallax shift against the background stars, the test of the day for distinguishing something nearby in the atmosphere from something genuinely among the fixed stars, and concluded it lay far beyond the Moon, in the region Aristotelian cosmology held to be permanent and unchanging.
The star, now known as Tycho's Supernova, SN 1572, faded from naked-eye visibility within about eighteen months, but the damage to the old cosmology was already done: a change in the supposedly changeless heavens had been measured, not merely observed, by an astronomer whose reputation for precision made the result hard to dismiss.
The queen's throne, in Greek myth a punishment for vanity, briefly held the brightest new light seen in Europe's sky in living memory, and helped end an idea about the sky that had stood for close to two thousand years.