Orrery - AbsoluteAstronomy.com

An orrery is a mechanical device that illustrates the relative positions and motions of the planet

Planet

A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...

s and moon

Natural satellite

A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....

s in the Solar System

Solar System

The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

in a heliocentric model

Model (physical)

A physical model is a smaller or larger physical copy of an object...

. 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

Earl of Orrery

Earl of Orrery is a title in the Peerage of Ireland that has been united with the earldom of Cork since 1753 . It was created in 1660 for the soldier, statesman and dramatist Roger Boyle, 1st Baron Boyle, third but eldest surviving son of Richard Boyle, 1st Earl of Cork...

— whence the name came. They are typically driven by a clockwork

Clockwork

A clockwork is the inner workings of either a mechanical clock or a device that operates in a similar fashion. Specifically, the term refers to a mechanical device utilizing a complex series of gears....

mechanism with a globe representing the Sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

at the centre, and with a planet at the end of each of the arms.

History

The first modern orrery was built circa 1704 by George Graham

George Graham (clockmaker)

George Graham was an English clockmaker, inventor, and geophysicist, and a Fellow of the Royal Society.He was born to George Graham in Kirklinton, Cumberland. A Friend like his mentor Thomas Tompion, Graham left Cumberland in 1688 for London to work with Tompion...

and Thomas Tompion

Thomas Tompion

Thomas Tompion was an English clock maker, watchmaker and mechanician who is still regarded to this day as the Father of English Clockmaking. Tompion's work includes some of the most historic and important clocks and watches in the world and can command very high prices whenever outstanding...

. 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

Prince Eugene of Savoy

Prince Eugene of Savoy , was one of the most successful military commanders in modern European history, rising to the highest offices of state at the Imperial court in Vienna. Born in Paris to aristocratic Italian parents, Eugene grew up around the French court of King Louis XIV...

. Rowley was commissioned to make another copy for his patron Charles Boyle, 4th Earl of Orrery

Charles Boyle, 4th Earl of Orrery

Charles Boyle, 4th Earl of Orrery KT PC FRS was an English nobleman, statesman and patron of the sciences....

, 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 mechanical models of the universe, correctly named planeteriums gained the name Orrery,

There were planetary machines before 1704, indeed according to Cicero

Cicero

Marcus Tullius Cicero , was a Roman philosopher, statesman, lawyer, political theorist, and Roman constitutionalist. He came from a wealthy municipal family of the equestrian order, and is widely considered one of Rome's greatest orators and prose stylists.He introduced the Romans to the chief...

, the Roman philosopher who was writing in the first century BC, Posidonius

Posidonius

Posidonius "of Apameia" or "of Rhodes" , was a Greek Stoic philosopher, politician, astronomer, geographer, historian and teacher native to Apamea, Syria. He was acclaimed as the greatest polymath of his age...

constructed a planetary model. The Antikythera mechanism

Antikythera mechanism

The Antikythera mechanism is an ancient mechanical computer designed to calculate astronomical positions. It was recovered in 1900–1901 from the Antikythera wreck. Its significance and complexity were not understood until decades later. Its time of construction is now estimated between 150 and 100...

, discovered in 1904 in 42m of water off the Greek island of Antikythera

Antikythera

Antikythera or Anticythera is a Greek island lying on the edge of the Aegean Sea, between Crete and Peloponnese. Since the 2011 local government reform it is part of the municipality of Kythira island....

and extensively studied, exhibited the diurnal motion

Diurnal motion

Diurnal motion is an astronomical term referring to the apparent daily motion of stars around the Earth, or more precisely around the two celestial poles. It is caused by the Earth's rotation on its axis, so every star apparently moves on a circle, that is called the diurnal circle. The time for...

s of the sun, moon, and the five known planets. The Antikythera mechanism is now considered one of the first orreries but for many decades was ignored as it 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 path as a simple circle. This could be modelled by the use of gears. Tycho Brahe's

Tycho Brahe

Tycho Brahe , born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations...

improved instruments made precise observations of the skies (1576-1601), and from these Johannes Kepler

Johannes Kepler

Johannes Kepler was a German mathematician, astronomer and astrologer. A key figure in the 17th century scientific revolution, he is best known for his eponymous laws of planetary motion, codified by later astronomers, based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican...

(1621) deduced that planets orbited the sun in ellipses. In 1687 Isaac Newton

Isaac Newton

Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...

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 need to represent a year length of 365.242 days, and using that to produce the cycles of the principal planets. As lated as 1650, P. Schirleus has produced a Geocentric planetarium showing the sun as a planet with Mercury and Venus moving around it as moons.

Joseph Wright

Joseph Wright of Derby

Joseph Wright , styled Wright of Derby, was an English landscape and portrait painter. He has been acclaimed as "the first professional painter to express the spirit of the Industrial Revolution"....

's picture "A Philosopher giving a Lecture on the Orrery in which a lamp is put in place of the Sun

A Philosopher Lecturing on the Orrery

A Philosopher Lecturing on the Orrery, or the full title, A Philosopher giving a Lecture on the Orrery in which a lamp is put in place of the Sun, is a painting by Joseph Wright of Derby depicting a lecturer giving a demonstration of an orrery to a small audience...

" (ca. 1766) which hangs in Derby Museum and Art Gallery

Derby Museum and Art Gallery

Derby Museum and Art Gallery was established in 1879, along with Derby Central Library, in a new building designed by Richard Knill Freeman and given to Derby by Michael Thomas Bass. The collection includes a whole gallery displaying the paintings of Joseph Wright of Derby; there is also a large...

, 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

Armillary sphere

An armillary sphere is a model of objects in the sky , consisting of a spherical framework of rings, centred on Earth, that represent lines of celestial longitude and latitude and other astronomically important features such as the ecliptic...

. The demonstration was thereby able to cover eclipse

Eclipse

An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer...

s.

To put this in context, it was in 1762 that John Harrison

John Harrison

John Harrison was a self-educated English clockmaker. He invented the marine chronometer, a long-sought device in solving the problem of establishing the East-West position or longitude of a ship at sea, thus revolutionising and extending the possibility of safe long distance sea travel in the Age...

's Chronometer

Chronometer

Chronometer may refer to:* Chronometer watch, a watch tested and certified to meet certain precision standards* Hydrochronometer, a water clock* Marine chronometer, a timekeeper used for celestial navigation...

allowed longitude

Longitude

Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....

to be accurately measured and also in 1766 that the astronomer Titius

Johann Daniel Titius

Johann Daniel Titius was a German astronomer and a professor at Wittenberg.Titius was born in Konitz , Royal Prussia, and died in Wittenberg...

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"

Eisinga Planetarium

The Eisinga Planetarium is an orrery, a working model of the solar system. It was built from 1774 to 1781 by Eise Eisinger in Franeker. The "face" of the model looks down from the ceiling of what used to be his living room, with most of the mechanical works in the space above the ceiling. It is...

was built from 1774 to 1781 by Eise Eisinga in his home in Franeker

Franeker

Franeker is one of the eleven historical cities of Friesland and capital of the municipality of Franekeradeel. It is located about 20 km west of Leeuwarden on the Van Harinxma Canal. As of 1 January 2006, it had 12,996 inhabitants. The city is famous for the Eisinga Planetarium from around...

, 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.

Explanation

All orreries are planetariums or planetaria (alternative plural). The term orrery has only existed since 1714. A grand orrery is one that includes the outer planets

Outer planets

The outer planets are those planets in the Solar System beyond the asteroid belt, which typically refers to these gas giant planets in order of their distance from the Sun:...

known at the time of its construction. The word planetarium

Planetarium

A planetarium is a theatre built primarily for presenting educational and entertaining shows about astronomy and the night sky, or for training in celestial navigation...

, (plural always planetariums) has been captured and now usually refers to hemispherical theatres in which images of the night sky are projected onto an overhead surface. Planetariums (orreries) can range widely in size from hand-held to room-sized. An orrery is used to demonstrate the motion of the planets, while a mechanical device used to predict eclipse

Eclipse

s and transits

Astronomical transit

The term transit or astronomical transit has three meanings in astronomy:* A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body, hiding a small part of it, as seen by an observer at some particular vantage point...

is called an astrarium

Astrarium

An astrarium, also called a planetarium, is the mechanical representation of the cyclic nature of astronomical objects in one timepiece. It is an astronomical clock.-Greek and Roman World:...

.

An orrery should properly include the sun, earth and the (earth's) moon (plus optionally other planets.) A model that only includes the earth, its moon and the sun is called a tellurion

Tellurion

A tellurion , is a clock, typically of French or Swiss origin, surmounted by a mechanism that depicts how day, night and the seasons are caused by the movement of the Earth on its axis and its orbit around the sun...

, and one which only includes the earth and moon a lunarium. A jovilabe is a model of Jupiter

Jupiter

Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

and its moons.

Planet	Mean Distance from the sun	Diameter	Mass	Density	No. of satellites	Orbital period	Inclination to ecliptic	Inclination of equator	Rotation rate
Mercury	0.39	0.4	0.05	5.1	0	0.24	7.0	?	59 days
Venus	0.72	1.0	0.9	5.3	0	0.61	3.4	23	243 days
Earth	1.00	1.0	1.0	5.52	1	1.00	0	23	1 day
Mars	1.52	0.5	0.11	3.94	2	1.88	1.9	24	24.5 hours

Jupiter	5.20	11	318	1.33	12	11.86	1.3	3	10 hours
Saturn	9.54	9.54	95	0.69	10	29.46	2.5	27	10 hours
Uranus	19.18	4	15	1.56	5	84.01	0.8	98	11 hours
Neptune	30.06	4	17	2.27	2	164.79	1.8	29	16 hours
Pluto	39.44	0.5?	?0.1	?	0	247.69	17.2	?	6 days

A planetarium will show the orbital period of each planet and the rotation rate, as shown in the table above. A tellurian will show the earth with the moon revolving around the sun. It will use the angle of inclination of the equator from the table above to show how it rotates around its own axis. It was show the earths moon, rotating around the earth. A lunarium is designed to show the complex motions of the moon as it revolves around the earth.

Orreries are usually not built to scale

Scale model

A scale model is a physical model, a representation or copy of an object that is larger or smaller than the actual size of the object, which seeks to maintain the relative proportions of the physical size of the original object. Very often the scale model is used as a guide to making the object in...

. Some fixed Solar System scale models

Solar system model

Solar System models, especially mechanical models, called orreries, that illustrate the relative positions and motions of the planets and moons in the Solar System have been built for centuries. While they often showed relative sizes, these models were usually not built to scale...

have been built and are often many kilometres in size.
A normal mechanical clock could be used to produce an extremely simple orrery with the Sun in the centre, Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

on the minute hand and Jupiter

Jupiter

on the hour hand; Earth would make 12 revolutions around the Sun for every 1 revolution of Jupiter. Note however that Jupiter's actual year is 11.86 Earth years long, so this particular example would lose accuracy rapidly. A real orrery would be more accurate and include more planets, and would perhaps make the planets rotate as well.

Projection orreries

Many planetariums (buildings) have a projection orrery

Planetarium projector

A planetarium projector is a device used to project images of celestial objects onto the dome in a planetarium.The first modern planetarium projectors were designed and built by the Carl Zeiss Jena company in Germany between 1923 and 1925, and have since grown more complex. Smaller projectors...

, which projects onto the dome of the planetarium a Sun with either dots or small images of the planets. These usually are limited to the planets from Mercury

Mercury (planet)

Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...

to Saturn

Saturn

Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...

, although some include Uranus

Uranus

Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...

. The light sources for the planets are projected onto mirrors which are geared to a motor which drives the images on the dome. Typically the Earth will circle the Sun in one minute, while the other planets will complete an orbit in time periods proportional to their actual motion. Thus Venus, which takes 224.7 days to orbit the Sun, will take 42 seconds to complete an orbit on an orrery, and Jupiter will take 11.86 minutes.

Some planetariums have taken advantage of this to use orreries to simulate planets and their moons. Thus Mercury orbits the Sun in 0.24 of an Earth year, while Phobos

Phobos (moon)

Phobos is the larger and closer of the two natural satellites of Mars. Both moons were discovered in 1877. With a mean radius of , Phobos is 7.24 times as massive as Deimos...

and Deimos

Deimos (moon)

Deimos is the smaller and outer of Mars's two moons . It is named after Deimos, a figure representing dread in Greek Mythology. Its systematic designation is '.-Discovery:Deimos was discovered by Asaph Hall, Sr...

orbit Mars

Mars

Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

in a similar 4:1 time ratio. Planetarium operators wishing to show this have placed a red cap on the Sun (to make it resemble Mars) and turned off all the planets but Mercury and Earth. Similar tricks can be used to show Pluto

Pluto

Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...

and its three moons.

Notable orreries

Shoemaker John Fulton

John Fulton

John Fulton may refer to:* John P. Fulton , American special effects supervisor and cinematographer* John Fulton , American author* John H...

of Fenwick, Ayrshire, built three between 1823 and 1833 - the last is in Glasgow's Kelvingrove Art Gallery and Museum

Kelvingrove Art Gallery and Museum

The Kelvingrove Art Gallery and Museum is a museum and art gallery in Glasgow, Scotland. The building houses one of Europe's great civic art collections...

.

The Franeker Planetarium

Eisinga Planetarium

built by a wool carder

Carding

Carding is a mechanical process that breaks up locks and unorganised clumps of fibre and then aligns the individual fibres so that they are more or less parallel with each other. The word is derived from the Latin carduus meaning teasel, as dried vegetable teasels were first used to comb the raw wool...

called Eise Eisinga in his own living room, in the small city of Franeker

Franeker

in Friesland

Friesland

Friesland is a province in the north of the Netherlands and part of the ancient region of Frisia.Until the end of 1996, the province bore Friesland as its official name. In 1997 this Dutch name lost its official status to the Frisian Fryslân...

, is in fact an orrery. It was constructed between 1774 to 1781. The "face" of the model looks down from the ceiling of a room, with most of the mechanical works in the space above the ceiling. It is driven by a pendulum clock, which has 9 weights or ponds. The planets move around the model in real time.

An innovative concept is to have people play the role of the moving planets and other Solar System objects. Such a model, called a human orrery, has been laid out with precision at the Armagh Observatory

Armagh Observatory

Armagh Observatory is a modern astronomical research institute with a rich heritage, based in Armagh, Northern Ireland. Around 25 astronomers are actively studying stellar astrophysics, the Sun, Solar System astronomy, and the Earth's climate....

Meccano Planetaria

The first Meccano Orrery was described in June 1918 Meccano

Meccano

Meccano is a model construction system comprising re-usable metal strips, plates, angle girders, wheels, axles and gears, with nuts and bolts to connect the pieces. It enables the building of working models and mechanical devices....

Manual, though it is the last quarter of the 20th Century that Alan Partridge, John Nuttall, Pat Briggs and Michael Whiting have experimented with the limitations and possibilty of this medium. There are six methods of building orreries:

Telescopic concentric tubing, though the tubing is not a Meccano part. For a full 9 planet system, 18 concentric tubes and 19 geared motions are needed
Nested hollow turntables with internal gearing. A 1984 Jovilabe showing Jupiter and the 14 then known moons required 14 tuntables and 324 gears; it is accurate to within 0.01%
Fixed central rod, with top drive and sun and planet gearing. In this method, the sun drives the first planet and this then drives the second and so on. The errors are thus cummulative, but non Meccano gearing can keep this with in 0.02%
Fixed central tube, with bottom drive and sun and planet gearing. This removes the need for an overhead gantry- improving the appearance
Two component epicyclic gearing.
Fixed Central Rod, Epicyclic gearing, top drive by 'by-pass gearing' from below.

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