Sirius (the Dog-Star) was the most important star to ancient Egyptian astronomers because it reappeared in Egypt each year just as the annual Nile flooding began. Sopdet was the goddess of this star. The Greeks called her "Sothis." The "Sothis Rising" coincided with the actual solar year only once every 1460 years. This astronomical event occured during the reign of the Roman emperor Antoninus Pius in AD 139. He commemorated it with a special coin. The time period between Sothic risings is called the Sothic Cycle and it is one of the tools Egyptologists use to create a chronology of Egyptian history.
As early as the 1st dynasty, Sopdet was called "the bringer of the New Year and the Nile flood." She was depicted as a human woman with a star on her head. She also guides the king to the afterworld, the Field of Rushes. In a 4th century BC papyrus, The Lamentations of Isis and Nephthys, Isis calls herself Sopdet and states that she will always follow Osiris in heaven.
Sopdet was the consort of Sah (the constellation Orion) and her son was Soped. This triad parallel Osiris, Isis and Horus. Therefore, in the Pyramid Texts, the king (in his Osiris form) copulates with his sister Sopdet, who gives birth to the planet Venus.
Sopdet was occasionally shown as a male, and was associated with Horus. In this form, Sopdet was one of the gods of the four corners of the earth and of the eastern frontier. As part of this duty, Sopdet would hold one of Nut's legs steady as her body arched over the earth.
Sirius (the Dog-Star) was the most important star to ancient Egyptian astronomers because it reappeared in 