Wednesday, April 16, 2008

The Constellations

According to Greek mythology, Queen Cassiopeia and her husband Cepheus once ruled over Ethiopia. One day Cassiopeia bragged that their daughter Andromeda was more beautiful than the Nereids, the daughters of the sea god, Nereus. When the Nereids complained to their father about Cassiopeia's arrogance, Nereus sent a sea monster to ravage the shore of Ethiopia. In desperation King Cepheus consulted the oracle of Delphi. There he was told that the only way to save his country was to sacrifice Andromeda to the monster. Andromeda was chained to a rock by the sea. However, salvation came at the last minute in the form of Perseus, who managed to subdue and kill the sea monster in a ferocious battle. As his reward Perseus received Andromeda in marriage and Ethiopia as her dowry. The gods later immortalized all the participants as constellations in the heavens, including the sea monster, which appears there as Cetus, the Whale.

This is just one of many stories told by ancient bards, stories whose protagonists the Greeks thought they recognized in the skies. These ancient people looked for bright stars and com­bined them in patterns that they then named after legendary figures. In the southern half of the celestial sphere, we find startlingly different names, such as Antlia, the Air Pump. Many of the southern constellations were not named until the eighteenth century, when astronomers no longer had much use for ancient mythology and preferred to elevate the most recent scientific inventions to the heavens one of which was the air pump.
From a number of different traditions modern astronomers have selected a total of 88 constellations and drawn up internationally recognized boundaries between them. Each constellation has its own characteristic shape. Today the constellations no longer have meaning beyond orienting the observer of the starry sky, they constitute a kind of "coordinate grid" of the sky.