The spherical astrolabe of Ptolemy

 The...“G.P.S.” of the stars of the ancient Greeks.  It was an exceptional astronomical instrument which depicted the celestial sphere and was used for the measurement of longitude and latitude of the observed stars from anywhere on Earth but also, vice versa, as locator of position (GPS) and also for the measurement of the Sun-Moon distance. It consisted of seven concentric articulated rings. The 7th ring (external) was fixed in the level of the meridian and had four marks that defined the horizontal and vertical. The 6th was calibrated and rotated freely in the level of the meridian with points 0° and 90° to represent the equator and the pole respectively and was placed in the direction of the Earth's axis. The 5th was directed towards the Sun. The 4th was articulated in the Earth's axis and observed the daily rotation of the astral sphere. The 3rd was calibrated and was articulated to the precedent at a distance of approximately 66° from the poles. It was placed in the ecliptic zodiac; it had the names of the star signs (zodiacs) and was used to read the longitudes of the stars. The 2nd was calibrated, revolved around a perpendicular axis in the level of the ecliptic and was used to read the latitude of the stars. Finally, the 1st ring (internal) had the aiming device.