Ptolemaic Epicycle Machine

What it shows:  Long before the time of Copernicus, the Greek astronomer Claudius Ptolemy created a model of all the planets' observed celestial motions. The model involved combinations of perfect circles rotating with uniform speed. Ptolemy explained the apparent "looping motion" of the planets by placing the center of one rotating circle, called the epicycle, which carried the planet, on another rotating circle, called the deferent, so that together the motions of the two circles produced the observed looping motion of the planet. Moreover, the...

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Kepler's Universe

Model of the solar system based on the five perfect solids.

What it shows:

Kepler attempted to describe the orbits of the planets in terms of the five regular polyhedrons. The polyhedrons, inscribed within one another define the distances of the planets from the Sun. They act as (invisible) supporting structures for the spheres on which the planets move. The order of the solids outwards from the Sun are the octahedron, icosahedron, dodecahedron, tetrahedron, and hexahedron.

How it works:

A contemporary illustration of...

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Kepler's Machine

Working model to show Kepler's 1st and 2nd laws and the equivalence of the area law to the law of equants.

What it shows:

A demonstration illustrating the equivalence of Kepler's second law, the Law of Areas, with the Law of Angles.

How it works:

In order to determine the orbit of Mars using circular orbits, Kepler had to offset the focus of Mars' orbit from the Sun to a point C (figure 1). Kepler's 2nd Law of planetary motion states that a planet's orbit around the Sun will sweep out equal areas in equal times....

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Armillary Sphere

Model to show celestial sphere; larger version has capacity to show lunar motions.

What it shows:

The position and motions of heavenly bodies are projected against a hypothetical sphere of infinite radius, centered on the Earth, called the Celestial Sphere. With this demo you can explain the motions of the stars and of the Sun, and show various aspects of the seasons.

How it works:

The main features of the sphere itself are shown schematically in figure 1. The spherical wire cage defines the celestial sphere, its...

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Eudoxos Hipoped Machine

Electrically driven machine to represent retrograde planetary motion according to Aristotle's theory of concentric spheres.

What it shows:

This is the realization of a proposed solution to retrograde motion put forward by Eudoxus (427 - 347 B.C.). Here a combination of three uniform circular motions produces retrograde motion.

How it works:

The hippopede machine consists of three concentric rings, with a point on the innermost representing the position of the planet. The assembly in figure 1 is held vertically in...

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Static model of site; can be used with light source to simulate a mid-summer's morning.

What it shows:

1:50 scale model of the Stonehenge site with the positions of Sun and Moon on important dates marked. It can be used with a light show to reproduce Sunrise on Midsummer's morning, June 21.

How it works:

The Stonehenge site consists of the sarsen circle of 30 megaliths capped with 30 lintels. Within this circle is a horseshoe pattern of five trilithons. 80m north-east of the circle's center is the Heel Stone; it is the...

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Equatorial Ring

Model of Ptolemy's ring used to measure the length of the year.

What it shows:

This is a model of the ring and method used by Claudius Ptolemy (2nd century A.D., Alexandrian astronomer) to determine the length of a year.


How it works:

The ring is...

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