Plate from 18th century encyclopedia showing an illustration of an elipsareon. The elipsaroen is an instrument invented for exhibiting the time, quantity, duration, and progress of solar eclipses, at all parts of the Earth. An equatorial mount is a mount for instruments that follows the rotation of the sky (celestial sphere) by having one rotational axis parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras. The advantage of an equatorial mount lies in its ability to allow the instrument attached to it to stay fixed on any object in the sky that has a diurnal motion by driving one axis at a constant speed. Such an arrangement is called a sidereal drive..