Speja Kaus Australis

Kaus Australis is the brightest star in the Sagittarius constellation. It's also the 36th brightest star in the night. 

Sagitta constellation is usually associated with the arrow that Heracles used to kill the eagle that Zeus sent to gnaw Prometheus' liver. In mythology, Prometheus moulded men and women out of clay in gods' likeness, and gave them fire that he had stolen from the gods. Zeus decided to punish him for this, and chained him to Mount Caucasus, where the eagle perpetually gnawed his liver, which would always grow again at night.

The eagle is represented by the neighbouring constellation Aquila. Heracles found Prometheus during one of his journeys, killed the eagle with an arrow, and freed Prometheus.

In a different myth, Sagitta is identified as the arrow Apollo used to kill the Cyclopes because they had made the thunderbolts of Zeus that killed Apollo's son Asclepius, the famous healer, who is represented by Ophiuchus constellation.

In yet another story, Sagitta is associated with the arrow of Eros which made Zeus fall in love with Ganymede, the shepherd represented by Aquarius constellation. In this story, Zeus' eagle guards the arrow in the sky.

The Greeks knew the constellation as Oistos, and the Romans later named it Sagitta.