What are constellations?

The first constellations were patterns of stars that ancient peoples used for navigation, timekeeping and storytelling. Most constellations used now, stem from patterns recognised by ancient Greeks and Romans, and they carry myths and legends from that time. However the ancient Greeks were not the first to recognise patterns. The 47 constellations they used were introduced by a Greek astronomer called Euxodus, who had learned them from priests in Egypt. They in turn had adopted them from Babylonian culture and they were originally created by the Sumerians around 2,000 BC. The oldest surviving star catalogue dates from

the 2^nd century AD and was written by the Greek astronomer Ptolemy. It records the position and brightness of one thousand stars, arranged in 48 constellations. In the 10^th century AD, an Arab astronomer updated this book and included many Arabic names for stars that are still used. No more constellations were added until the end of the 16^th century, when Dutch explorers sailed to the East Indies. From there they could observe the southern sky that was below the horizon in Europe. Two Dutch navigators, Pieter Dirkszoon Keyser and Frederick de Houtman, catalogued nearly 200 new stars and formed twelve new constellations. Other astronomers filled in the gaps between those constellations and nowadays the sky is divided into 88 areas, or constellations. The names and boundaries were officially agreed on by a resolution of the International Astronomical Union in 1930. The constellation names are in Latin, although several are derived from the Greek.

Sixty-eight of those constellations are visible from South Africa, the other twenty lay above +30 degrees and are therefore always below the horizon. Along those twenty constellations are Ursa Major and Ursa Minor, the best known constellations of the northern hemisphere. Although at some point in winter we can see a few stars of Ursa Major, very low on the horizon.
Most people know, at least by name, the twelve constellations of the Zodiac that are used in astrology. The Zodiac is the band of stars along the ecliptic through which the Sun, Moon and planets move. Here in the southern hemisphere the Southern Cross is the most famous constellation.

Until next time, clear skies,
Miriam