Cassiopeia

The Queen's W

Cassiopeia is one of the few constellations whose shape matches its pattern on any chart: five stars of second and third magnitude in a zigzag. Depending on the hour and season it looks like a W, an M, a 3 or a sigma.

It lies in the Milky Way, the band of our galaxy seen edge on, so the background is crowded with faint stars. That makes the area a rewarding place to sweep slowly with binoculars.

How to find it

Find Polaris first, using the Big Dipper's pointers. Then continue across Polaris about the same distance on the other side: the W is there. The Dipper and Cassiopeia sit on opposite sides of the pole, like two ends of a clock hand, so when one is low the other is high.

On autumn evenings Cassiopeia is near the zenith from 40°N, while the Dipper hugs the northern horizon. In spring the roles reverse. A line from Polaris through Caph, the westernmost star of the W, continues toward the Great Square of Pegasus and Andromeda.

Main stars and their names

Schedar (Alpha Cas) comes from Arabic for 'breast'. It is an orange giant about 230 light-years away. Caph (Beta Cas) means 'hand', from an old Arabic picture of a hand stained with henna spread across these stars.

Gamma Cassiopeiae, the middle star of the W, has no traditional name in wide use. It is a hot, fast-spinning star that throws off gas and changes in brightness without warning, sometimes outshining Schedar. Ruchbah (Delta Cas) means 'knee', the queen's knee as she sits on her throne. Segin (Epsilon Cas) completes the W.

In 1572 the Danish astronomer Tycho Brahe saw a 'new star' near the W that grew about as bright as Venus. It was a supernova, an exploding star, and it helped show that the heavens were not unchanging.

Deep-sky objects for binoculars and small telescopes

M103 lies about 1 degree from Ruchbah. In binoculars it is a small, tight patch; a small telescope resolves a fan of stars. Not far away, NGC 457 is nicknamed the Owl Cluster or ET Cluster, because two bright stars look like eyes and two lines of stars like outstretched arms.

M52 sits off the other end of the W, on the line from Schedar through Caph extended about the same distance again. It is a rich cluster that looks like a soft glow in binoculars.

Between Cassiopeia and Perseus lies the Double Cluster, two bright groups side by side. It is officially in Perseus, but many observers find it by starting at Cassiopeia.

Mythology

In Greek myth Cassiopeia was the queen of Aethiopia and wife of King Cepheus. She boasted that she or her daughter Andromeda was more beautiful than the Nereids, the sea nymphs. Poseidon sent a sea monster, and Andromeda was chained to a rock as a sacrifice until Perseus rescued her.

As punishment, Cassiopeia was placed in the sky on her throne, circling the pole so that she spends part of each night upside down. Her whole family surrounds her: Cepheus, Andromeda, Perseus and Cetus, the monster. Arab astronomers also saw a camel in part of the pattern, and some Sámi traditions in northern Europe saw these stars as part of an elk-hunting scene.

Practical observing tips

Look in the northeast on early autumn evenings, or high overhead in November. The W is bright enough for city skies, so it is a good second pattern to learn after the Big Dipper.

Take binoculars to a dark site and sweep along the Milky Way from Cassiopeia toward Perseus. Note the colors: Schedar looks orange next to the bluish-white Gamma Cas. Because Gamma Cas varies, comparing it with Schedar over months is a simple project for beginners.