In Greek mythology, King Cepheus ruled a kingdom in the southeastern Mediterranean. Cepheus had a remarkably beautiful queen named Cassiopeia, and their daughter Andromeda inherited the queen’s beauty. Whenever the three appeared together, their beauty invariably drew everyone’s attention. Cassiopeia was convinced that no one could rival her beauty and could not help marveling at her own reflection each day. However, the seemingly peaceful kingdom fell into crisis because of a single remark made by Cassiopeia.
One day, while Cassiopeia was combing her beautiful long hair in front of a mirror, she said to herself, “I must be the most beautiful woman in the world, even the sea nymphs are not as beautiful as I am.” The remark soon reached the ears of the sea nymphs. Enraged by Cassiopeia’s arrogance and vanity, they asked Poseidon to punish her.
Poseidon then sent the sea monster Cetus. The creature was as enormous as an island. Its whale-like tail helped it move swiftly through the sea, while its powerful movements could raise enormous waves capable of destroying coastal buildings. With its enormous jaws open, Cetus came to Cepheus’s kingdom and began ravaging the coast, leaving Cepheus desperate for guidance from the gods.
The oracle declared that the disaster would end only if Andromeda were sacrificed to the monster. After a painful struggle, Cepheus had no choice but to chain his beloved daughter to a rock by the sea.
As the monster drew closer, Andromeda could not break free from the chains and could only weep helplessly. At that moment, a man happened to pass by: the hero Perseus. After hearing what had happened, Perseus took up his sword and resolved to rescue Andromeda from the monster. When Perseus plunged the sword into the creature’s body, Cetus twisted violently in an attempt to throw Perseus off. Perseus clung tightly to Cetus, holding on despite the monster’s furious thrashing. Bleeding heavily from the repeated attacks, the monster eventually sank into the sea.
After the ordeal, Andromeda fell in love with Perseus, who had rescued her from danger, and the two eventually held a grand wedding. Later, the figures of Cepheus, Cassiopeia, Andromeda, Perseus, and Cetus were placed among the stars. Together, they portray the story of the Cepheus family in the autumn sky.
Observation Guide
Few bright stars are visible in the autumn night sky. Looking toward the northeast reveals Cassiopeia, a constellation shaped like the letter W. Connecting the stars at the two ends of the W and extending the line outward about five times that distance will lead you to Polaris.
To the northwest of Cassiopeia is Cepheus, an irregular pentagon resembling a short pencil.
South of Cassiopeia lies Andromeda, whose main stars form a rough arc. M31, the Andromeda Galaxy, is a spiral galaxy and the largest galaxy in the Local Group.
East of Andromeda lies Perseus, which appears roughly Y-shaped.
Variable Stars
When the night sky is observed from Earth, some stars appear to change in brightness over time. Such stars are called variable stars.
One of the earliest recorded variable stars is Algol, located in the constellation Perseus. Algol is a system composed of multiple stars. Although it appears to be a single star when viewed from Earth, it actually consists of two main stars orbiting each other. When the dimmer star passes in front of the brighter star, it blocks part of the light, causing Algol to appear dimmer. Once the eclipse ends, its brightness returns. Because the two stars orbit each other regularly, Algol’s brightness also changes periodically. Variable stars whose brightness changes because one star periodically passes in front of another are called eclipsing varieables.
Another well-known type of variable star is the Cepheid variable. The name comes from Delta Cephei, a star in the constellation Cepheus. Cepheid variables do not change in brightness because another star passes in front of them. Instead, the stars themselves periodically expand and contract. This regular change is known as stellar pulsation. When a star expands, its surface temperature decreases; when it contracts, its surface temperature increases. As the star’s size and temperature change, so does the amount of light it emits. As a result, it appears to brighten and dim periodically when observed from Earth.
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Easter Egg
Chomp, chomp, chomp! Chomp, chomp, chomp! Chomp, chomp, chomp!
Crocquado kept biting through the net,
freeing the whale and allowing it to return to the ocean.
