equatorial mount
A mounting for astronomical telescopes having two axes, one of which revolves about an axis that is parallel to the axis of the Earth's rotation. This axis can be driven by a motor at a rate equal to the diurnal motion of the celestial object being viewed, allowing the telescope to keep the object in view for long periods without adjustment. The other axis, perpendicular to the first, has free movement that allows the telescope to be pointed anywhere in the sky. Compare altazimuth mount.