the armagh observatory human orrey

Mark E. Bailey, David J. Asher, and

Apostolos A. Christou

The Armagh Observatory Human Orrery

RAS, London, 13 January 2006 1

[email protected]

http://star.arm.ac.uk

The Armagh ObservatoryHuman Orrery

Mark E. Bailey, David J. Asher

and


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Leiden, 2006 Oct. 12

The Human OrreryAn orrery is a dynamic solar system model

• designed to illustrate the heliocentric world-view

In a Human Orrery people become the planets• the whole of solar system astronomy can be

investigated in a fun way “on the ground”

The simplest Human Orreries are not to scale• e.g. planets on circular orbits; no accurate link to

the planets’ true positions in space versus time! => only a limited range of activities possible

They become more interesting when laid outwith greater care

• e.g. the Dynic Astropark Human Orrery (Japan)

The Human Orrery is as versatile as a sundial• the Armagh model has an accurate scale of 1:150

billion, and a fixed time-step of 16 days! it shows the 6 classical planets,1 asteroid and 2

comets at any time! it includes the 13 ecliptic constellations, as well as

directions to more distant objects in the Universe

Dynic Astropark Human

Orrery (c.1997)





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Why “Orrery”?Invented around 1704 by George Graham(c.1674–1751)

• he gave a copy (or its design) to John Rowley(1674–1728), the celebrated London instrumentmaker

Rowley made a copy for Prince Eugène ofSavoy

• he then made another for his patron, CharlesBoyle, the fourth Earl of Orrery

Charles Boyle (1674–1731)• author, soldier and statesman

• grandson of Roger Boyle (1621–1679), the firstEarl of Orrery! a son of Richard Boyle, the first (or Great) Earl of

Cork (1566–1643)! in his day, “one of the richest men on the planet”

The name “orrery” for such a model waspopularized by the Irish essayist Sir RichardSteele (1672–1729)

Images © Science Museum

and National Portrait Gallery

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Rowley’s Orrery, in Science Museum





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John, Fifth Earl of Cork andOrrery (b.1707)

Orrery, invented by Graham 1700. Improved by

Rowley and presented by him to John, Fifth Earl of

Orrery, after whom it was named at the suggestion

of Richard Steele

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Ground-Based Astronomy for All…

Each orbital tile shows variousastronomical data• the name; tile number; date;

distance from Sun; eclipticlongitude; and true anomaly

With a simple “key” shown onthe central Sun-tile





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Principal FeaturesThe Armagh Human Orrery shows:

• the elliptical orbits and changing positions ofvarious solar system objects versus time! provides an accurate “map” of the solar system,

giving users a better “feel” for the Earth’sposition in space

! enables all of Kepler’s laws to be discovered bydirect measurement; the times of meteorshowers from the two comets; and much more…

• the relative orbital periods and positions of thedifferent orbital objects

• the thirteen ecliptic constellations throughwhich the Sun passes in a year! which ones are visible at different times of year

! and that the First Point of Aries is in Pisces!

• the directions to more distant objects in theUniverse! facilitating discussion of the variety of different

“animals” in the astronomical “zoo”

Most important, it is fun to use!

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Location in the ObservatoryGrounds





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Overview of Human Orrery

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Some Orrery Activities“Walking the Orrery” and “Running the Orrery” (andhow fast can you go…)

• investigating Kepler’s third law

Finding the planets “tonight” (or at any other date)• and discovering which can be seen after dark at

night, or as morning or evening stars

• investigating conjunctions, oppositions andalignments; and the visibility of distant stars

Measuring angles and distances between objects• working out distances and speeds in space

• investigating Kepler’s laws by direct measurement

• investigating the mathematics of orbital motion andof ellipses (areas, circumferences etc.)

• using a “map” with a scale of 1:150,000,000,000

Learning new mathematical and calendrical concepts

• counting (more than 200 tiles!)

• modular arithmetic (e.g. 14 tiles for Venus etc.)

• ratios of planetary orbital periods (e.g. 8/13 V/E)

• “leap steps”, “leap stops” and Leap Years





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Other Activities and GamesHistory, design, teamwork, dance and play!

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Summary and ConclusionsThe Armagh Human Orrery (http://star.arm.ac.uk/orrery)• a dynamic solar system model where people become the

moving objects

• the first outdoor exhibit to show with precision the orbits andpositions of the main solar system bodies

• engages people in maths, space science and astronomy! introduces key concepts of astronomy, as well as pointers to more

distant objects in the Universe, in a fun and entertaining way

• brings “heaven down to Earth”; provides an improvedunderstanding of Earth’s changing position in space! encourages people to observe the sky, and to compare what they

see from “Earth” — on the ground — with what they see from Earth— in the sky

• facilitates a wide range of interdisciplinary activities! e.g. ranging from history, astrology and the development of

astronomy, to dance, physical exercise and design

• easy to make, easy to use, and as versatile as a sundial





[email protected]

http://star.arm.ac.uk

AcknowledgementsWe thank especially Miruna Popescu and Brendan Owens for their help

with images and other material

Astronomy at Armagh Observatory is fundedby the Northern Ireland Department of

Culture, Arts and Leisure

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Orbital Periods, Leap Stepsand Leap Stops

1184STOP67**29.45710759.23Saturn**

15413STOP27**11.8624332.589Jupiter**

23050STOP21*4.60391681.592Ceres*

3016STEP431.8808686.980Mars

66STEP231.0000365.256Earth

1423STOP140.6152224.701Venus

125520STEP5.50.240887.969Mercury

Number ofEarth

Years forStep/Stop

Numberof Orbitsfor Leap

Step/Stop

Leap Stepor LeapStop?

Numberof Tiles

per Orbit

OrbitalPeriod(years)

OrbitalPeriod(days)

Planet

*Tiles every 80 days

**Tiles every 160 days





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Find the PlanetsThe Human Orrery can show where the planets are at any time.To do this use the Earth as a key.

STEP 1: Find the nearest Earth tile for the chosen time of year. For

example, Earth is at tile number “14” on August 13 of any year. Keep thisEarth tile number (“14”) in your head.

STEP 2: Find the Start Tile for the chosen planet and year using the table.This gives the planet’s position on January 1 for each year. For example, on2010 January 1 Jupiter is at tile “114” and Mercury is at tile “4”.

Positions of orbital objects on January 1 for each year.

STEP 3: Go to the Start Tile and move forward the same number of stepsas the Earth tile number from STEP 1. In the case of Jupiter, steppingforward 14 tile-steps brings you to tile “128”. Note that the tiles for Jupiterand Saturn are marked every ten steps so that you must find the next closesttile (“130”) or make a rough estimate of tile position. For the two comets andthe asteroid, tiles are marked every 5 steps.

For Mercury, be careful to follow the order of tiles, which are interleaved.Also, when tile “0” is reached (for Mercury or any other planet) you mustcontinue around the orbit again. For Mercury, in this example, you shouldreach tile “7” for 2010 August 13 after moving forward 14 steps.

Earth in SpaceChoose an object and a date (for example, Mars on 2010 August 13). Usethe method described above to locate the Earth and the object at this time.Now stand on the Earth’s tile and look towards the central Sun tile.

If the planet is to the left of the Sun tile, then it will be visible from Earth asan “evening star”. If it is to the right, it will be visible as a “morning star”. If it

lies beyond the Sun tile, or (in the case of Mercury and Venus) possiblybetween the Earth and the Sun, then it will be a daytime object and not visibleat night. If the planet is behind you (i.e. opposite the Sun in space), then itwill be visible all night. Planets can be seen when the sky is clear, so you cancheck your result on the next clear night.

You may find cases when planets appear to line up in the same direction asseen from Earth or another vantage point in space. This is a planetarygrouping or alignment. For example, Mercury, Venus and Saturn were closelyaligned at tile numbers “0”, “11” and “11”, as seen from Earth (tile “11”), on2005 June 26.

Looking farther afield, beyond the solar system, the Human Orrery shows thethirteen (not twelve) zodiacal constellations traversed by the Sun in thecourse of a year, the constellation boundaries, and the directions to a varietyof more distant objects in the Universe. You can use the Human Orrery todiscover when these constellations and other objects can be seen at night.

Positions of the six classical planets for a range of interesting dates.

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Walking the OrreryFirst, choose a planet and find its Start Tile, for example the tile labelled “0”, which is theplanet’s position on 2005 January 1. Now move from tile 0 to 1 to 2 and so on. Eachstep corresponds to 16 days of time. Repeat this for other planets to see how theirspeed changes with distance from the Sun. If you are part of a group, each person can bea di!erent planet and you can walk the orrery in lock-step on the call of a group leader.

Note that the asteroid Ceres and the two comets (Encke and Halley) are shown every fivetime-steps (80 days), and Jupiter and Saturn every ten time-steps (160 days).

When you come to the last tile of a given orbit, make sure you move on to the next tile,labelled “0”, and start counting 0 to 1 to 2 again. Also, observe that Mercury’s eleventiles represent two revolutions of that planet around the Sun.

“Walking the Orrery” shows that planets nearer the Sun move faster. You can also seewhen planets come close to one another or line up as seen from Earth or another pointon the orrery. In fact, the Human Orrery provides an accurate “map” of the solar system,enabling all the laws of planetary motion to be discovered by direct measurement on theground.

What is an Orrery?An orrery is a dynamic model of the solar system. The Human Orrery is an orrery inwhich people play the role of the moving planets. The first orrery, a mechanical device,was invented around 1704 by the English clockmaker George Graham (c.1674–1751).This showed the Earth and Moon orbiting the Sun, but later models showed all the knownplanets.

The name “Orrery” comes from the patronage of Charles Boyle (1674–1731), the fourthEarl of Orrery, Co. Cork, who commissioned a copy of the first orrery from the Londoninstrument maker, John Rowley. The Armagh Human Orrery is the first outdoor exhibitto show with precision the elliptical orbits and changing positions of the planets andother solar system objects with time.

With this exhibit, you can imagine you are a planet, asteroid or comet, and follow its patharound the Sun. You can investigate the laws of planetary motion, work out the positionsof the planets at any time, their distances from one another and when they are visiblefrom Earth. The model also shows the directions from Earth of more distant objects inthe Universe.

Sun TileAt the centre of the Human Orrery lies the Sun tile. This presents a key to theinformation on the orbital tiles. The letter r denotes the distance from the Sun inastronomical units (AU), where 1 AU is approximately 150 million kilometres. The scaleof the Human Orrery is 1:150 billion, so 1 metre on the ground corresponds to 1 AU inspace.

The true anomaly f is the angle measured around the orbit from the object’s point ofclosest approach (perihelion) to the Sun. L denotes the ecliptic longitude of the object,measured anti-clockwise from the direction of the First Point of Aries, which is shown onthe Sun tile and also on the plaque fixed to the Robinson Dome. As viewed from Armagh(in the northern hemisphere) all the planets revolve around the Sun anti-clockwise, in thedirection of increasing L. On the Human Orrery only Comet Halley revolves in aclockwise, “retrograde” direction.

The Human OrreryThe small yellow dot at thecentre of the Sun tilerepresents the size of theSun (about 1.4 million km)on the scale of the HumanOrrery.

The orbital tiles showdata such as tilenumber, date, andthe values of L, r, andf.





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Observatory Grounds and Astropark

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Education and PublicOutreachExhibitions, Tours, PublicLectures, Open Days• library, archives and rare books

• public lectures, school andundergraduate work experience

• developing Observatory Grounds,Astropark, and Human Orrery





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Some Historic Instruments

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Why Astronomy?!Underpinned by three main strands of interest:• the broadly “religious” or cosmological strand

! the quest to understand our “Origins”, Man’s place in the Universe

• the broadly “practical” strand, i.e. commercial, military, oreconomic “spin-off” from astronomy, including education! e.g. the Calendar; Navigation; Celestial Mechanics; Earth

Observation; Image Processing; the “Inspiration” of Astronomy

• the broadly “scientific” strand of curiosity driven research intoMathematics, Planetary Science and Astrophysics! the project, no less, to understand the nature, contents and

interactions of all the objects in the entire Universe…

We live at an exceptional time: a “Golden Age” in whichactivity in all these areas is at an all-time high• provides astronomy with a rare conjunction of opportunity

• contributes to the unprecedented advances in observationand theory (the former almost always leading the latter)





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Location of the ArmaghObservatory

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Montage Overview of HumanOrrery





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Overview of Human Orrery

the armagh observatory human orrey

Education

human orrery people

human orreryan orrery

armagh human orrery

unawe workshop leiden

rowleys orrery

orrery andhow

orrery activitieswalking

armagh model