The once and future north star
This week we go on a quest to find the celestial dragon, Draco. Winding through a patch of the northern sky between Ursa Major and Ursa Minor, Draco is neighbor to the strongman, Hercules. Star lore from ancient Greece connects Draco to Hercules and his twelve labors. The dragon is also mentioned as taking part in the battle waged between the Gods and the Titans for supremacy and control of Mount Olympus.
One of Ptolemy’s original 48 constellations, Draco is the 8th largest star pattern in the sky. Even through it covers such a large area, star gazers may have trouble locating it because the stars outlining the dragon’s form are fairly dim. Thousands of years ago, one of those stars named Thuban was the north star. Its proximity to the north celestial pole influenced the alignment, architecture and artwork found in a number of structures built by ancient Egyptians.
In 2500 B.C., the circumpolar stars were the same as the ones we see today. But, during those times Thuban was the north star instead of Polaris. This difference is due to a phenomenon called precession. Our planet has an axial tilt of about 23.5 degrees from vertical. But, the direction that Earth’s axes point slowly changes. It takes about 26,000 years to make a complete circle around and back to where we are now. Think of how a top slowly wobbles without falling over and you get a better idea of how precession works.
The ancient Egyptians knew the star patterns we call the Big Dipper and Draco as Meskhetiu (leg of the bull, Seth) and the Hippopotamus, respectively. The stars near the north celestial pole were collectively known as Ikhemu-sek or the ‘imperishable’ because their circumpolar motion causes them to never rise or set.
As Egyptologists worked to understand the ancient culture, shafts leading skyward from the burial chambers of the Great Pyramid of Cheops presented a bit of a puzzle. Earlier claims that the shafts were used for ventilation were pushed aside in the early 1960’s when a celestial alignment was proposed. The northern shaft of the king’s burial chamber points toward Thuban, Meskhetiu and the Hippopotamus. The southern shaft points toward where Orion would have been located in the ancient sky. The stars of Orion were linked to the ancient god of death and resurrection, Osiris.
Artwork found in the tomb of Tutankhamen depicts a ceremonial retelling of the battle between Horus, son of Osiris and Seth, the bull. Seth is associated with evil and chaos. In the battle Horus loses an eye and the bull, is slaughtered. Seth is transformed into a Hippopotamus. The battle reaffirms the authority of Osiris, the cycle of death-resurrection and the triumph over chaos and evil.
Other examples of ancient artwork show seven stars surrounding the leg of Seth. The severed leg was fabled to give new life to the dead. Tethered to a chain held by the Hippopotamus, the leg is represented by the seven stars of the Big Dipper rotating about the fixed axis of the north celestial pole.
To the ancient Egyptians, the Pharaoh was a demi-god and the circumpolar stars were the king’s destiny for the afterlife. In death, the king would ascend to the stars, gain immortality and maintain the order of the cosmos.
