It is a great time of the year to search out Capricornus, the sea goat. This constellation was identified a few thousand years BC in Babylonian astronomy as the goat-fish, a hybrid creature with the body and head of a goat and the tail of a fish. In Greek mythology, the constellation is often associated with either Amalthea, who suckled Zeus, or Pan, the shepherd god.
This week, the brightest object by far in the constellation is the planet Saturn. The chart shows the image looking south from London at midnight as 12 September becomes 13 September. Compare the brightness of Saturn with the brightest star in Capricornus: Deneb Algedi, just off to the east. Then carefully trace out the constellation.
The challenge comes when you reach its western extent and the star Algedi. Look carefully and you will see that this is a double star, with a fainter companion star tucked in close to the more obvious main star. Telescopes have also revealed a third star in this system. Capricornus is easily seen from the southern hemisphere in the north-western sky.
