Orrery - History

History

According to Cicero, the Roman philosopher who was writing in the first century BC, Posidonius constructed a planetary model.

The Antikythera mechanism, discovered in 1900 in a wreck off the Greek island of Antikythera and extensively studied, exhibited the diurnal motions of the sun, moon, and the five known planets. The Antikythera hand driven mechanism is now considered one of the first orreries but for many decades was ignored as it was thought to be far too complex to be genuine and was not mentioned in the 1967 Science Museum booklet. It was heliocentric and used as a mechanical calculator designed to calculate astronomical positions.

Copernicus in De Revolutionibus Orbium Coelestium published in Nuremberg in 1543 challenged the Western religious teaching of a geocentric universe where the sun rotated around the earth. He found that some Greek philosophers had proposed a heliocentric universe. This simplified the apparent epicyclic motions of the planets, making it feasible to represent the planets' paths as simple circles. This could be modeled by the use of gears. Tycho Brahe's improved instruments made precise observations of the skies (1576–1601), and from these Johannes Kepler (1621) deduced that planets orbited the sun in ellipses. In 1687 Isaac Newton explained the cause of this motion in his theory of gravitation.

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

The first modern orrery was built circa 1704 by George Graham and Thomas Tompion. Graham gave the first model (or its design) to the celebrated instrument maker John Rowley of London to make a copy for Prince Eugene of Savoy. Rowley was commissioned to make another copy for his patron Charles Boyle, 4th Earl of Orrery, from which the device took its name. This model was presented to Charles' son John, later the 5th Earl. Its importance was partially in that a mechanical model of the universe, correctly named a planetarium, gained the name Orrery,

Joseph Wright's picture "A Philosopher giving a Lecture on the Orrery in which a lamp is put in place of the Sun" (ca. 1766) which hangs in Derby Museum and Art Gallery, features a group (three men, three children, and a lone woman) listening to a lecture by a 'natural philosopher'—the only light in the otherwise darkened room is from the "sun" in the brass orrery, which, in this case, has rings that cause it to appear to be similar to an armillary sphere. The demonstration was thereby able to cover eclipses.

To put this in context, it was in 1762 that John Harrison's Chronometer allowed longitude to be accurately measured and also in 1766 that the astronomer Titius first 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 ... The numbers refer to astronomical units, that is 1.496 x 10⁸ km (93 x 10⁶ miles). The Derby Orrery does not show mean distance, but demonstrated the relative planetary movements: all part of a process understanding contemporary cutting edge scientific thinking.

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

In 1764, Benjamin Martin devised a new type of planetary model, where the planets were carried on brass arms leading from a series of concentric or coaxial tubes. With this construction it was difficult to make the planets revolve, and to get the moons to turn around the planets. Martin suggested that the conventional orrery should be consist of three parts: The planetarium where the planets revolved around the sun, the tellurian which showed the inclined axis of the earth and how it revolved around the sun, and the lunarium which showed the eccentric rotations of the moon around the earth. In one orrery, these three motions could be mounted on a common table, separately using the central spindle as a prime mover.