《宋史·志·卷一》
极度极星在紫微垣，为七曜、三垣、二十八宿众星所环绕，这叫北极，是天的正中。
极度极度极星之在紫垣，为七曜、三垣、二十八宿众星所拱，是谓北极，为天之正中。
The extreme North Star is in the Purple Forbidden City, surrounded by seven stars, three Y垣, and twenty-eight constellations, which is called the North Pole and is the center of the sky.