Written records of navigation using stars, or celestial navigation, go back to Homer's Odyssey where Calypso tells Odysseus to keep the Bear (Ursa Major) on his left hand side and at the same time to observe the position of the Pleiades, the late-setting Boötes and the Orion as he sailed eastward from her island Ogygia traversing the Ocean. The Greek poet Aratus wrote in his "Phainomena" in the third century BC detailed positions of the constellations as written by Eudoxos. The positions described do not match the locations of the stars during Aratus' or Eudoxos' time for the Greek mainland, but some argue that they match the sky from Crete during the Bronze Age. This change in the position of the stars is due to the wobble of the Earth on its axis which affects primarily the pole stars. Around 1000 BC the constellation Draco would have been closer to the North Pole than Polaris. The pole stars were used to navigate because they did not disappear below the horizon and could be seen consistently throughout the night.