Solar system model

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Jupiter at South Station, part of Museum of Science, Boston scale model. This was also used in FETCH! with Ruff Ruffman

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. The enormous ratio of interplanetary distances to planetary diameters makes constructing a scale model of the solar system a challenging task. As one example of the difficulty, the distance between the Earth and the Sun is almost 12,000 times the diameter of the Earth.

If the smaller planets are to be easily visible to the naked eye, large outdoor spaces are generally necessary, as is some means for highlighting objects that might otherwise not be noticed from a distance. The objects in such models do not move. Traditional orreries often did move and some used clockworks to make the relative speeds of objects accurate. These can be thought of as being correctly scaled in time instead of distance.

One scale model, designed to be easily replicated, is called The Thousand-Yard Model^[1] and spans about a kilometre. In it, the Earth is represented by a peppercorn. A school class building this model might tape the peppercorn to an index card to make it more visible. Another scale model is the 1:10 000 000 000 model, in which 100,000 km is represented by 1 cm. In this model, the Sun is 600m from the Kuiper belt and dwarf planet Pluto. The largest scale model in the world is the Sweden Solar System.

In July 2005 the Austrian art group monochrom placed the planets true to scale (sun, 4 meters in diameter at Machine Gallery, Alvarado Street, near Echo Park) throughout the Los Angeles cityscape. Then they conducted an 'illegal space car race' through the solar system.

In regional Australia, in the area surrounding Coonabarabran (Australia's Astronomy Capital) there is a model solar system that reaches from the Observatory (The Sun) to surrounding towns and localities.

In the US, a precedent-setting model solar system project the Voyage National Program began with installation of Voyage on the National Mall in Washington, DC, in front of the Smithsonian museums. It is a 1:10 000 000 000 scale model approved by the US Commission of Fine Arts and National Capital Planning Commission. It was designed for replication and permanent installation in communities across the nation. It was also designed as a center-piece for sustained community-wide science education, embracing a "Learning Community Model" of programming for students, teachers, families, and the public. Grade K-12 lessons available for download enhance the exhibition experience. Voyage is now permanently installed in Kansas City, Houston, and Corpus Christi. It is approved for installation in Des Moines, Orlando, and Baltimore, and a dozen other sites are exploring it as a site feature in their community. For the International Year of Astronomy 2009, Voyage has now become available worldwide as "the Voyage International Program" with storyboard translation into any language. The Voyage National Program also has a Facebook page with photoalbums for all the Voyage communities.

In 2009, to celebrate International Year of Astronomy, the Scottish Solar System project created an approximate scale model of the Solar System, with correctly scaled objects representing the major planets sited temporarily, for Autumn Moonwatch week (Oct 24th - Nov 1st 2009) at the locations of a number of Scottish amateur astronomy groups and societies. In this model the Sun was represented by the main building of Glasgow Science Centre. The Scottish Solar System project was coordinated by Dr Martin Hendry, astronomer at the University of Glasgow, and Glasgow Science Centre. Although the model did not include Pluto (which on the same scale would be located roughly in the Faroe Islands), its scale of 1:8,200,000 was smaller than any other model listed in the table below. On the same scale the nearest star beyond the Solar System, Proxima Centauri, would still lie nearly 5 million km from Glasgow Science Centre!

[edit] Scale models in various locations

Several towns and institutions have built outdoor scale models of the solar system. Here is a table comparing these models.

[edit] A model based on a classroom globe

A classroom globe

Relating the size of the Solar system to familiar objects can make it easier for students to grasp the relative distances. Most classroom globes are 41 cm (16 inches) in diameter. If the Earth were reduced to this size, the Moon would be a 10 cm (4 in) baseball floating 12 metres (40 feet) away. The Sun would be a beach ball 14 stories tall (somewhat smaller than the Spaceship Earth ride at Epcot) floating 5 kilometres (3 miles) away. While a complete model to this scale has never been built, a solar system built centered in Washington DC, London, or Sydney, to that scale (approximately 1:31,000,000) would look like this:

If the scale of the above model is increased to 1:310,000,000, i.e. all distances and sizes reduced by a factor of 10, then the Earth and Venus can be modeled by ping pong balls, the Moon and smaller planets by various size marbles or lumps of modeling clay, the gas giants by balloons or larger playing balls, and a circle the diameter of the Sun can be drawn on the floor of most classrooms. The scale distance to α Centauri would be 1/3 of the way to the Moon.

[edit] A model based on a sports field

Relating the size of the Solar System to familiar objects can make it easier for students to grasp the relative distances. Most American schools have a football field associated with the high school (100 yards or 92 meters long). Other schools may have a soccer field nearby (90 to 120 m long). If the Sun was reduced to slightly less than one inch (21 mm), Pluto would be a 0.002 inch (0.05 mm) speck floating 100 yards (91.4 meters) away. Jupiter would be less than three-thirty-secondths of an inch (2.38 mm) in diameter and would sit on the 13 yd (11.88 m) line. Uranus would be less than one-thirty-secondth of an inch (0.79 mm) sitting nearly on the 50 yd (45.72 m) line. At that scale, the speed of light would be about 1 inch every 5 seconds (5 mm per second). Light takes about 5.5 hours to go from the Sun to Pluto. Here is what the Solar System built to that scale would look like. This complete model would be simple to make with scale planets taped to wood stakes or metal rods. The scale is approximately 1:64,700,000,000.

[edit] A model for primary school children

Relating the size of objects to the planets can be difficult for children, particularly if the objects are so small that they cannot be seen. The Scale below is 10 x (times) the scale above, which is a convenient size, virtually all of the objects can be seen. At this scale the distance from the sun to Pluto is just under 1 km (metric units only). At this scale, the speed of light would be about 50 mm per second. Light takes about 5.5 hours to go from the Sun to Pluto. The scale is approximately 1:6,470,000,000. At this scale the Sun could be represented by a children's soccer ball, and α Centauri A is about the size of an adult soccer ball. The smaller planets are about the size of "hundreds and thousands" (which vary in size from less than 1mm to close to 2mm). Even at this scale α Centauri A is on another continent or at the centre of the earth, a distance of about 6,300km.

Children can have some fun with this model, for example Mercury could be a small red "hundred and thousand" while earth might be a larger blue "hundred and thousand". Venus might be smaller. Children can look for two small red "hundreds and thousands" for Mercury and Mars. To maintain relativities Mercury should be slightly smaller than Mars etc. The objects can be assembled in the classroom and then taken outside to a large park.

[edit] Misleading models

Major features of the solar system, distances of centers of the planets to a modified logarithmic scale. Terrestrial planets are 10 times enlarged.

The models sketched here are an eye opener to many people interested in, but not knowing much about astronomy. They are far cry from the drawings of the solar system one usually sees in books or on the internet, such as the one to the right. Even if it is stated in the text that the layout is not to scale, it is often difficult for the reader to fully comprehend how discrepant the scale of the distances in the image is compared to the sizes of the objects depicted.

[edit] See also

• Numerical model of solar system
• Orrery

[edit] References

[edit] External links

• A list of websites related to solar system models
• An online scale model (does not work in some browsers)
• An article about a temporary exhibit in Melbourne, Australia
• A map with solar system models in Germany

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