Celestial pole

As the celestial poles and the points of intersection of the Earth's axis will be referred to the celestial sphere. The north celestial pole is the point near the Polaris ( α Ursae minoris ) in the constellation Ursa Minor ( Little Dipper or ) to the seemingly turns the heavens in its diurnal motion; the south celestial pole is opposite to him, in his presence, however, lies only a faint star, σ Octantis.

The celestial pole is - in the long periods of time - not stable. On the one hand, the Earth's axis shifts due to the precession in 26,000 years along a large cone around the pole of the ecliptic, on the other hand varies its intersection point with the earth's surface to about 10 feet (see polar wandering ).

Equatorial coordinate system

On the celestial sphere on which the astronomy defines the equatorial celestial coordinates right ascension and declination, the celestial poles are properly aligned with the geographic North Pole (or South Pole ).

In the celestial poles, the hour circles converge, as the meridian passing an observation location by the celestial poles. The north celestial pole corresponds to a declination of exactly 90 ° -90 ° of the south pole.

Polar wandering

By the effect of the precession of the celestial pole in the course of traveling from 25,800 years ( the cycle of precession ) around the Ekliptikpol (in the center of the images ). This movement takes on a circle of about 23 ° pole spacing, which corresponds to the current " obliquity of the ecliptic ". Around 5000 years ago was Thuban ( α Draconis the main star in the dragon ) the polar star, and then the faint Kappa Draconis and before about 3000 years Kochab in the Little Bear. Today it is the star Alpha Ursae Minoris or Polaris ( North Star ). From the year 3000 the north celestial pole is located in the constellation Cepheus. In about 12,000 years, the bright new Wega Polaris (but about 6 degrees away from the true north celestial pole ) will be.

Miscellaneous

All stars move on their apparent daily Railways ( Earth's rotation in 23:56:04 hours) on a circular path exactly in the direction of a position angle of 90 °.

For calibration of photometers has rings defines a group of fixed stars around the north celestial pole, the Polsequenz or North Polar sequence. Their apparent brightness was measured accurately and covers an area from the 4th to the 10th magnitude.

The position angle for specifying directions between double stars or directions of movement refers to the respective direction from the star to the north celestial pole.