The story behind the name Cassiopeia (courtesy of the Harvard-Smithsonian Center for Astrophysics) is as follows:
Cassiopeia is named after the queen of a country on the northern coast of Africa, Aethiopia (not modern Ethiopia). She boasted that she and her daughter Andromeda were more beautiful than the Nereids, the 50 sea nymph attendants of Thetis, the sea goddess, and Poseidon, the sea god. Thetis, and Poseidon's wife Amphitrite (an alternate sea goddess), were also Nereids, so Cassiopeia's boast was an insult to the gods. The Nereids begged Poseidon to punish Cassiopeia. Poseidon sent a flood carrying a sea monster to destroy the kingdom. Cassiopeia's husband, King Cepheus consulted an oracle, who told him that the only way to appease Poseidon and stop the monster was to sacrifice Andromeda. Andromeda was chained to a sea cliff to be eaten by the monster. She was rescued by the hero Perseus who had seen her chained to the cliff and had fallen instantly in love with her. Perseus was returning from carrying out his oath to kill the Gorgon, Medusa. Perseus offered to kill the sea monster and rescue Andromeda in return for her hand in marriage. Cepheus and Cassiopeia agreed reluctantly. They had already agreed to marry her to Cephus's uncle (his father's twin brother Agenor), and once she had been rescued, they tried to break their promise to Perseus.
Andromeda wanted to keep their promise and insisted that the wedding be held immediately. In some versions of the myth, Cassiopeia summoned Agenor, who rushed into the wedding party with armed men. Perseus fought off a number of them but was greatly outnumbered. He picked up Medusa's head (which he was bringing back as proof that he killed her) and when his attackers looked at it, they turned to stone. Poseidon is supposed to have set images of Cepheus and Cassiopeia in the sky. As a punishment for her treachery, her constellation (a zig-zag shape like an "M" or "W") is supposed to represent Cassiopeia either chained to her throne (in an ironic reference to her daughter's ordeal) or stuffed into a basket. Because the constellation is in a circumpolar position (meaning that it seems to revolve centered around the pole star, Polaris), Cassiopeia is at times suspended upside down in the sky in a very undignified position.
And now for a little science:
Cassiopeia contains five major stars: Caph, Shedir, Tsih, Ruchbah, and Segin. These stars make up the “M” or “W” that you see in the constellation. These stars are all different distances from Earth.
Caph: 54 light years
Shedir: 229 light years
Tsih: 613 light years
Ruchbah: 99 light years
Segin: 442 light years
To put this into perspective for those that don’t understand what light year means look at it this way: If Caph were to explode RIGHT NOW we would not know for 54 years. Another way to look at it is like this: You build a spaceship able to travel at the speed of light (186,000 MILES PER SECOND) and start flying toward Caph. It will take 54 years to get there.
Within the constellation there are two stars that are extremely rare yellow hypergiants. Yellow hypergiants are massive stars that are 20-50 times the mass of our Sun. These stars consume nuclear fuel extremely fast and therefore only remain as “stars” for a few million years. Once the stars run out of fuel they destroy themselves in supernovas or hypernovas.
Cassiopeia is not alone in the sky. Some of related and notable constellations surrounding her are the constellations Cepheus (her husband), Perseus (the demigod warrior), Andromeda (her daughter), and Pegasus (the flying horse).
Thanks for reading! I hope you were able to learn something.