'Sirius and Orion sailing across the sky at Dendera.'
Sirius and Orion are sailing across the firmament in boats on the astronomical ceiling in the outer hypostyle hall of the Hathor Temple at Dendera. The ceiling consists of seven separate strips but here we are looking at a detail of the upper register of the EASTERNMOST STRIP.
The star Sirius, or Sothis as it was known by the Egyptians, is depicted here as a reclining cow on a boat but the star was also identified with the goddess Isis. The rise of Sirius on the eastern horizon, after a few weeks of invisibility, signaled the beginning of the summer Nile flood for the Egyptians and the beginning of the New Year.
The second boat carries a god who personifies the constellation Orion, or Sahu as he was called by the Egyptians. The text above the god describes him as 'Sahu, the soul (ba) of Osiris' and thus it can be understood that Osiris is looking back at his wife Isis (in the shape of a cow) to see if she is following him across the sky. Orion/Osiris as a god looking back first appears in Egyptian iconography in stars clocks on coffin