So…What’s An Orrery?

A Philosopher Lecturing on the Orrery, 1776 – Joseph Wright of Derby

Its a strange name but an orrery is a mechanical device that demonstrates the motions and relative positions of the planets and moons in the Solar System in a heliocentric model.

They are typically driven by a motor or a clockwork mechanism with a globe representing the Sun at the centre, and with a planet at the end of each of the arms. An orrery can be seen as a scale model of our solar system, it can range widely in size from hand-held to room-sized..

Though the Greeks had working planetaria, the first orrery that was a planetarium of the modern era was produced in 1704, and one was presented to the Earl of Orrery — whence the name came.


The first modern orrery was made circa 1704 by Thomas Tompion and George Graham. Graham gave the first model or its design to the celebrated device maker named John Rowley, who lived in London,in order to produce a copy for Prince Eugene of Savoy. Rowley produced another one for his patron Charles Boyle, 4th Earl of Orrery, from which the model took its name. This device was given to Charles’ son John as present, later the 5th Earl. Its importance was partially in that mechanical scale models of the solar system and the universe, correctly named planetariums gained the name Orrery.

A clockwork orrery

There were planetary models before 1704, indeed according to Roman philosopher Cicero, who was writing in the first century BC, Posidonius made a planetary model. The Antikythera mechanism, which was discovered in 1904 in 42m of water off the Greek island of Antikythera, illustrated the five known planets and the diurnal motions of the sun, moon.

 Antique Orreries

The Antikythera mechanism is now considered to be one of the earliest orreries, but was not mentioned in the 1967 Science Museum booklet. For many years The Antikythera mechanism was ignored, because it seemed too complex to be genuine. It was geocentric, used as a mechanical calculator designed to calculate astronomical positions.

In the Western religious teaching of a geocentric universe,the sun rotated around the earth,but Copernicus in De Revolutionibus Orbium Coelestium published in Nuremberg in 1543 challenged this. He found that a heliocentric universe had been proposed by some Greek philosophers.

This simplified the apparent epicyclic motions of the planets and make it feasible to represent the planets path as a simple circle, which could be modelled by the use of gears. Tycho Brahe’s improved devices made precise observations of the skies (1576–1601), from which Johannes Kepler (1621) proved that planets orbited the sun in ellipses. The cause of this motion was explained in Isaac Newton’s theory of gravitation In 1687.

Christian Huygens calculated the gear trains which were needed to represent 365.242 days year length, and using which to make the cycles of the principal planets. As late as 1650, P. Schirleus has made a Geocentric planetarium ,it showed the sun as a planet with Mercury and Venus moving around it as moons. Christian Huygens built a heliocentric planetary model while resident in Paris between 1665 and 1681, and in 1703 he published details of the model.

Chronometer Measurements

A picture hangs in Derby Museum and Art Gallery named “A Philosopher giving a Lecture on the Orrery in which a lamp is put in place of the Sun” by Joseph Wright (ca. 1766), features three children, three men, and a lone woman, listening to a lecture by a ‘natural philosopher’— the only light is from the “sun” in the brass orrery, which, in this case, has rings that cause it to look like an armillary sphere. The demonstration was thereby able to show eclipses.

To put this in context, longitude was allowed to be accurately measured by John Harrison’s Chronometer in 1762,and also in 1766 Titius first who was an astronomer demonstrated that the mean distance of the planets could be represented by the progression .

That is, 0.4, 0.7, 1.0, 1.6, 2.8, 5.2, 10.0 … The numbers refer to astronomical units, that is 93 x 10^8 miles(1.496 x 10^8 km). The Derby Orrery doesn’t show mean distance, but demonstrated the relative planetary movements: all part of a process understanding contemporary cutting edge scientific thinking.

The Planetarium

Eisinga’s “Planetarium” was made from 1774 to 1781 in his home in Franeker, in the Netherlands. This “Planetarium” displays the planets across the width of a room’s ceiling, and has been in operation almost continually since it was built. This orrery was a planetarium in both senses of the word- firstly a complex planetary instrument, and secondly it was displayed in a special room, which was a sort of theatre for observers. the Dutch Royal family, by who gave him a pension, bought Eisinga house.

A 1766 Benjamin Martin Orrery, used at Harvard

A ‘New’ Orrery

Benjamin Martin created a new type of planetary instrument in 1764. In this new planetary instrument the planets were carried on brass arms leading from a series of coaxial or concentric tubes. With this construction it was difficult to get the moons to turn around the planets, and to make the planets revolve.

Benjamin Martin thought that there were three parts that the conventional orrery should consist of: The lunarium which showed the rotations of the moon around the earth, the tellurian(tellurion) which showed the inclined axis of the earth and how it revolved around the sun, and the planetarium where the planets revolved around the sun.

In an orrery, these three motions could be assembled on a common table and separately using the central spindle as a prime mover.

Read previous post:
Rare ‘Supermoon’ Total Lunar Eclipse This Week

The first "supermoon" lunar eclipse in more than three decades...

Crowdfunding To Save Australia’s Mopra Radio Telescope

A team of astronomers have resorted to raising funds through...

Australian Student’s Ion Space Drive Beats NASA Design

Space engines might soon become far more resourceful: An Australian...