Cassiopeia
Cassiopeia, the W-shaped signpost for finding the North Star. Here Tycho's nova blazed in 1572 and opened the door to modern astronomy.
Science
The scienceStanding opposite the North Star from the Big Dipper, this W-shaped constellation is used, along with the Dipper, to locate Polaris. In 1572 a nova (SN 1572, "Tycho's Star") blazed forth here, bright enough to be seen even in daylight; the event shattered the Aristotelian view of an eternal, unchanging heaven and became a decisive turning point in the birth of modern astronomy.
Mythology
How it became a constellationCassiopeia, queen of Ethiopia, drew the wrath of the gods by boasting that her daughter Andromeda was more beautiful than the nymphs of the sea. Poseidon sent the sea monster Cetus to threaten the kingdom, and an oracle demanded that Andromeda be offered as a sacrifice. Though the hero Perseus rescued Andromeda, Cassiopeia was punished by being bound to her chair and hung in the sky, made to wheel around for half of every year hanging upside down.
Observing Guide
how to observe🔭 How to find it
In the northern sky, look for a distinct "W" (or an upside-down M) formed by five bright stars, and you have found Cassiopeia. It lies directly opposite the Big Dipper with Polaris between them, so in autumn and winter, when the Dipper is hard to see, it serves as a guide to the North Star. The pointed middle of the W (the star Gamma) roughly points toward Polaris.
✨ What to look for
Straddling the heart of the Milky Way, Cassiopeia is unusually rich in open clusters. The bright, star-packed M52 and NGC 457 — called the "Owl Cluster" or "ET Cluster," with two bright stars gleaming like eyes — are the standouts. Beyond these, M103 and several NGC clusters are scattered near the W, so even just sweeping with binoculars keeps turning up new knots of stars.
📍 Where to see it (US · Canada · UK · Australia)
Cassiopeia's W is circumpolar from the US, Canada and UK, never setting and visible on every night of the year; it rides highest, near the zenith, on autumn evenings (September–November) and hangs low in the north in spring, wheeling around Polaris through the night. From Australia it is effectively invisible — its stars lie too far north (declinations above +56°) ever to clear the horizon from Sydney and most of the continent.