Astronomy and Astrophysics

Astrobrella

Umbrella decorated with the constellations.

What it shows:

The aberration of starlight is the shift in the position of the image of a star due to the rotation of the Earth about the Sun, and is a consequence of the finite velocity of light. For a star directly overhead, a telescope will have to be angled by v/c to the vertical where v = velocity of the Earth in space, in order that the telescope be pointing at the star. The equipment necessary to show aberration is one umbrella.

How it works:

The best way to picture this...

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Local Group of Galaxies

Lights-up-in-the-dark three-dimensional model of the local group.

What it shows:

Three dimensional model of the local group of galaxies, with a scale of 1mm = 1kpc.

How it works:

A large wooden base board forms an x-y plane from which the approximate relative positions of the local galaxies are measured. The galaxies are LEDs and (for the two biggest, the Milky Way and Andromeda) 6V bulbs, mounted atop 8mm diameter plastic tubing; the length of the tube gives a z-axis position of the galaxy. The wires from the LEDs and...

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Spiral Galaxy

Hand held Plexiglass model of spiral galaxy.

What it shows:

Handy size model of a generic spiral galaxy to show salient features or to describe structure of the Milky Way

How it works:

The model is a 30cm diameter Plexiglass disc 1cm in thickness, with a Ping-pong ball stuck through the center to represent the nucleus. The spiral arms of the galaxy are sprayed on with white paint, and we've stuck on a "you are here" arrow pointing to the outer reaches of one of the spiral arms at the approximate position of the Sun in the...

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Binary Star

Two small closely mounted bulbs simulate resolution problems.

What it shows:

The ability to resolve two closely separated stars depends upon the aperture size of the observing instrument. Here two tiny bulbs represent stars that are barely resolvable by human eyes across the lecture hall.

How it works:

The light collected from two stars by the eye (or by a telescope mirror) are themselves geometric point sources but are circular diffraction fringes

The light from a distant star is not detected as a geometric point...

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Jupiter's Satellites

Static model of satellite orbits.

What it shows:

Static 3-D model showing the orbital paths of Jupiter's satellites.

How it works:

The model marks the orbital paths of the Jovian satellites to a scale of 1.5cm = 106 km. This scale allows the orbit of the outermost satellite Sinope to fit within a 1m × 1m plywood base. The orbits of the outer 8 satellites are marked using loops of 2mm × 1mm spring steel supported to their correct heights by 5mm Plexiglas rods (Pasiphae rising to the greatest height of 42cm). The...

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Centrifugal Eggbeater

Spinning frame that demonstrates equatorial bulge (oblateness).

What it shows:

The rotation of a planet about its axis causes its equator to bulge due to the "centrifugal force" acting on its mass. Here a spinning wire frame simulates the effect.

How it works:

Planets are actually oblate spheroids rather than spheres due to their rotation. This device consists of two spring metal rings mounted on a metal axis. The north pole is free to slide so that, as the frame spins, the hoops flatten and the equator bulges. The axis is...

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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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Stonehenge

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.

ring

How it works:

The ring is...

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Moon Orbit Model

Mechanical model of Earth-Moon orbit around Sun.

What it shows:

A model to demonstrate the precession of the Moon's orbit relative to the ecliptic. It is useful for discussing the conditions necessary for the occurrence of an eclipse.

How it works:

A large aluminum disk represents the plane of the Moon's orbit about the Earth. The disk lies flush with the box surface it sits in; the plane of the box representing the Ecliptic. The Moon's own orbit is inclined at 5° to the ecliptic, and precesses with an 18 year period. You...

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Precession Globe

Globe pivoted so north pole can precess.

What it shows:

Due to the oblateness of the Earth, the gravitational force between the Earth and the Sun sets up a couple which causes the Earth's axis of rotation to precess. An adapted globe shows what is meant by precession.

How it works:

An old 8" (19cm) globe has been modified 1 to allow it to precess on its axis. A 23° cone is cut into the south pole, and a cone of metal supported by a metal equatorial ring has been inserted. This makes the globe bottom heavy (and...

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Elastic Light

What it shows: 

The redshifted spectrum of galaxies and quasars is due to an expanding universe and can be expressed as the ratio of the scale factor of the present Universe to that of the Universe when the light was emitted. You can think of this as the light being s-t-r-e-t-c-h-e-d as the Universe expands so it arrives with a longer wavelength.

How it works: 

A 50cm × 10cm strip of dental dam with a wave drawn on it, attached at one end to a post and the other end free to pull. A wooden dowel at the pulling end ensures...

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