The movement of constellations

It seems that the movement of the constellation with the celestial sphere is caused by the movement of the earth itself, in which the rotation and revolution of the earth are the most obvious changes in the starry sky. Due to the rotation of the earth, the starry sky background rotates once a day around the celestial axis; The starry sky also changes slowly with the seasons. A year has passed, and the starry sky is almost the same as it was a year ago. The rotation axis of the earth's rotation also has a long-term motion, called precession, with a period of about 25,765 years. This movement causes the periodic drift of the North Pole in the background of stars, which is called precession in astronomy. A cursory observation of the constellation in a short time can ignore this movement.

The stars are moving at high speed. The motion of stars can be decomposed into the radial velocity of their connection direction and the self-nature perpendicular to it, in which the self-nature will change the apparent position of stars in the starry sky. Because the star is too far away from the earth, it can generally be considered that the position of the star in the sky is fixed.

Because the apparent positions of the sun and planets relative to the earth are not fixed with the positions of the background stars on the celestial sphere, they periodically pass through the 13 constellation on the ecliptic. In astrology, it is often described as "Mercury is in Scorpio". However, there are only twelve constellations in astrology, and they are equally divided.