The Human Orrery

Historical background
Structure of the Orrery
Orrery quiz
Links to rest of Armagh Orrery site and external sites

The Human Orrery is the latest addition to the grounds of Armagh Observatory and provides a unique investigation of planetary motion. It is also fun to use with the capacity to present fundamental ideas in astronomy, mathematics and space science to as wide an audience as possible.

Full size version of this photo of the Human Orrery by Miruna Popescu is over 3 Megabytes

A Brief Historical Background

The first orrery was conceived by English clockmaker and inventor George Graham (c.1674-1751) around 300 years ago. This initial model only showed the earth-moon system which orbits our Sun. Graham gave the design of this original model to the celebrated London instrument maker John Rowley, who was commissioned to make one for his patron Charles Boyle (1674-1731). Boyle's patronage of Rowley soon led to the elaboration of Graham's invention so that it included all the known planets and some moons of the solar system. The origin of the term "orrery" is explained when we consider the title Boyle held - the fourth Earl of Orrery (Orrery being the old name for a part of Co. Cork).

Mechanical orrery by Gilkerson, in Armagh Observatory

Structure of the Human Orrery

Armagh Observatory's Human Orrery is interactive: it allows people to play the part of the moving planets. It features an accurate scale model of the positions and orbits of the Earth and the five other planets in the Solar System known since ancient times (Mercury, Venus, Mars, Jupiter and Saturn), as well as the asteroid Ceres and two comets: 1P/Halley and 2P/Encke. The orbits of these objects are arranged on the ground with stainless steel tiles. Jumping from one tile to the next represents a 16 day time interval for all the planets, except Jupiter and Saturn, whose tile jumps represent a 160 day interval. The tiles for Ceres and the comets have 80 day intervals. More distant objects which could not be accommodated within the dimensions of the Human Orrery are listed on the Outer Ring of the exhibit.

At the centre of the Orrery lies the Sun Tile (figure to the left, above). This defines some of the data available on any of the orbital tiles (similar to the figure on the right, above). What follows is a table for this data with an explanation of each quantity:

Symbol	Name	Explanation
r	Distance to Sun	This figure, measured in AU (astronomical units), is the distance from the planet to the Sun
	The First Point of Aries	This is the direction towards the Sun as seen from Earth at the northern spring equinox (currently March 20th). Because of the phenomenon known as precession of the equinoxes, the First Point of Aries presently lies in the constellation Pisces, not Aries.
L	Ecliptic Longitude	This angle is measured anticlockwise from the First Point of Aries
f	True Anomaly	This is the angle to the object, measured around the orbit, from the object's perihelion (position closest to Sun)

The orbital tiles give other information not indicated on the Sun Tile including: the symbol for the object, tile number and corresponding date. The scale of the Human Orrery is one metre to the Astronomical Unit (AU), or approximately 1:150 billion. (1 AU = 1.58 × 10^-5 light years = 150 billion metres.)

Further Website Content

Human Orrery Quiz

The "How to" Guide for Navigating the Human Orrery

The Outer Ring of the Human Orrery

Zodiacal constellation boundaries

Human Orrery photographs from Miruna Popescu

Artistic representation of objects in the Human Orrery

Live Webcam of the Human Orrery

Links to .pdf documents containing further information about the Human Orrery:

1st Leaflet: The Human Orrery

2nd Leaflet: A Tour of the Human Orrery

Presentation at EPSC 2009