An Etymological Dictionary of Astronomy and Astrophysics
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A star that lies on the → rotation axis of the Earth in the north hemisphere. The → Pole Star is not, in the long term, permanently fixed to the → celestial pole. This is because of the Earth's → axial precession which gradually moves the celestial poles in the sky. It takes about 26,000 years for the precession to turn the pole a full circuit. Currently the North Pole Star is → Polaris, which will continue to mark the north celestial pole for several more centuries. But, around 4,000 B.C. → Gamma Cephei will become the North Pole Star. Around 7,500 B.C., → Alderamin will take up the role. And it will be the brilliant → Vega's (Alpha Lyrae) turn in about 12,000 years. In the past, about 3,000 B.C., → Thuban (Alpha Draconis) was the North Pole Star. Then → Kokab (Beta Ursae Majoris) became the Pole Star from 1500 B.C. to 500 A.D. before leaving the task to Polaris.

→ north; → pole; → star.

A star that lies along the Earth's → rotation axis. The term usually refers to the star → Polaris, which is the current → North Celestial Pole star. The → South Celestial Pole is not currently associated with any bright star. See also: → North Pole Star, → South Pole Star.

→ pole; → star.

A star that would mark the south → celestial pole. Presently no bright visible star is situated along the → rotation axis of the Earth in the southern hemisphere. But, because of the Earth's → axial precession, about 7,000 years from now the star → Delta Velorum in the constellation → Vela, the Sail, will come to within 0.2 degrees of the South Celestial Pole (around the year 9250 B.C.). That is closer to marking the celestial pole than → Polaris or → Sirius ever do during their reigns as pole stars! Sirius will become the South Pole Star some 60 thousand years from now (around the year 66270 B.C.). In that time, Sirius will come to within 1.6 degrees of the South Celestial Pole.

→ south; → celestial; → pole.