The first orrery was made in 1712, by Thomas Wright of London, and was used to demonstrate and explain the motions of the Earth and Moon around the sun. In time, it became normal practise to include the known planets also.
This finely designed and executed modern orrery has been constructed to show the various relationships between the planets, the moon and the sun, as well as to predict "phenomena" such as eclipses and conjunctions. One turn of the ebony handle represents two days on earth and shows night and day, as well as - via the blued-steel star chart - the differing aspects of the night sky as the earth proceeds through the year. The leap year counter indicates when the four year cycle is completed and an extra day is added to the year. This is represented by the pointer's jumping back a day on the horizon and thus corrcting itself. In addition, since the axis of the earth is correctly inclined to an angle of 23.5°, the changing of the seasons, the equinoxes, and the six months of day followed by six months of night at the North Pole are all accurately demonstrated also.
The moon rotates around the earth and is geared to rotate on an inclined plane differing to that of the earth around the sun by 5°. The nodes of the moon - those points where the moon passes through the plane of the ecliptic and thus causes an eclipse - are marked on the steel disc which controls the moon's plane of rotation, which in turn is geared to rotate relative to the stars once in every 6,794 days. The ebonised hemisphere represents the moon's shadow and hence demonstrates the various phases and changing shape as observed from the earth. In fact there are several more variations in the moon's behaviour - such as libation - but of such a subtle nature as would not be possible to show on a model of this size.