What is an Orrery?
An Orrery is a planetary model of our Solar System. Typically an Orrery shows the first 6 planets circling the sun. Starting closest to the sun, these are: Mercury, Venus, Earth, Mars, Jupiter and Saturn. Sometimes some of the moons of a planet are also shown. The “Jovian” – By turning the handle of this model, you can witness the revolutions of the 6 planets known to ancients. In this kind of planetarium, the sizes of the heavenly bodies and the distances between them are not to scale. This is because the true dimensions in the Solar System do not lend themselves to a linear down-scaling… For instance, if we make the diameter of the smallest and innermost planet – Mercury, 1mm across, then the sun would need to be 30cm across, the distance from the sun to Mercury 1.2m, and the distance from the sun to Saturn 29 metres!! Not only would this be very difficult to engineer, it would also be very difficult to look at. Hence the Orrery does not scale size and distance. However in a geared
An orrery is a model of the solar system which is designed to show the locations of the various planets and their relationships to each other. Using internal clockwork and gearing, the orrery can be made to move, demonstrating the rotational patterns of various bodies in the solar system. These devices are sometimes called planetariums, which can be confusing for people who associate planetariums with large domes onto which various images are projected. Archaeological evidence suggests that the concept of the orrery is quite ancient; the Greeks, for example, made several devices which resemble orreries. Production of these devices really took off in the 18th century, when a famous orrery was commissioned for Charles Boyle, the Fourth Earl of Orrery, and people began to take more interest in the solar system and the objects which inhabit it. A high quality orrery today can fetch a high price, as the construction techniques required to build one are quite demanding; a handful of artisans
An Historical Background. Until the time of Copernicus (1543) primitive man looking at the stars in the sky, would conclude that they were fixed to the surface of a rotating sphere. Of course we now know this to be untrue but it is still useful to create a map of the stars on the surface of a sphere, indicating the various directions of the stars. Globes to represent the stars in the sky have constructed from an early date. When methods of producing globes are considered some convention needs to be adopted to transfer printing from a plane surface to a sphere in order to elliminate any distortions. Traditionally, (certainly before 1509), this involved printing onto pieces of specially shaped paper called gores (wide in the middle with two pointed ends). Approximately 12 of these would then be wrapped around the sphere with the points at the two poles. The celestial globe represents the stars as seen from outside the sphere and not as seen from the Earth. The globes were pivoted in orde
A planetary model of our Earth/Moon system around the Sun. This usually includes some movements in a third dimension, such as the inclination of the Moon’s orbit or the Earth’s axis fixed in space. A model that shows the planets revolving round the Sun, normally without any planetry rotation or axial tilt, is called a Planetarium.
An orrery is, quite simply, a mechanical model of the solar system. To see some superb examples visit www.orrerymaker.com which is the website of Brian Greig who specialisies in creating facsimilies of historical scientific instruments. Quite often an orrery is used in teaching children the basics of how the solar system works and many schools encourage children to make their own.
