We’ve probably all heard that Thuban was the North Star when the pyramids were built, and that Vega was the North Star thousands of years before that. That’s because the Earth’s axis wobbles like a top on a table, drawing a big circle in the sky with a period of about 26,000 years. It’s just a happy accident that Polaris sits so close to the Earth’s north rotational axis today. Within a thousand years it will be 7° away from…