Tag Archives: Precession

Draco (The dragon)

Draco, Ursa MinorDraco is a large constellation of rather dim stars that is also one of the 48 constellations cataloged by 2nd century astronomer Ptolemy. Since it is a circumpolar constellation at 40 degrees north latitude, it is visible on any night at any time, but it reaches its highest nightfall ascension in January. Draco’s tail starts near the northernmost pointer star of the Big Dipper, and it roughly parallels the curvature of the Big Dipper handle before curving under the Little Dipper and turning back toward the south, and then terminating at the dragon’s head. The best chance of seeing this constellation will be under a very dark sky.

Thuban (Alpha Draconis), is the most interesting star in Draco. Six thousand years ago, when the Egyptian pyramids were build, Thuban was the Earth’s pole, or north star, and the Egyptians built north-facing entrances on the pyramids that were aligned to this star. Due to precession, the large circle that the Earth’s axis traces among the fixed stars every 26,000 years, Polaris has temporarily supplanted Thuban as the pole star. The most notable deep sky object in this constellation is the Cat’s Eye Nebula (NGC 4563).

IAU Draco Chart, IAU and Sky $ Telescope (Roger Sinnott and Rick Fienberg), June 5, 2011.
IAU Draco chart, IAU and Sky & Telescope magazine (Roger Sinnott and Rick Fienberg), June 5, 2011.

© James R. Johnson, 2014.