The hour axis (also right ascension axis ) is a term from astronomy and describes the axis of an equatorial telescope mount around which the telescope can track the daily rotation of the starry sky .
If aligned exactly, the hour axis represents the local parallel to the earth axis and thus points exactly to the celestial pole of the respective hemisphere.
It also designates one of four possible degrees of freedom of an astronomical telescope . All the stars seem to rotate around this axis. If you track the telescope (manually or by motor), you can follow the course of a star (sun, planet, star, etc.). One rotation does not take place in 24 hours, but around 4 minutes faster (see sidereal day and sidereal time ).