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 1:6 300 000 000 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.
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Several towns and institutions have built outdoor scale models of the Solar System. Here is a table comparing these models.
| Location | Scale | Sun dia. | Earth dia. | Sun-Earth | Sun-Pluto |
|---|---|---|---|---|---|
| Actual statistics | 1:1 | 1.392 Gm | 12.76 Mm | 149.6 Gm | 5.914 Tm |
| Scottish Solar System Project, (was a temporary installation) | 1:8 200 000 | 170 m | 1.56 m | 18.3 km | 551 km (Neptune) |
| Sweden Solar System | 1:20 000 000 | 71 m | 65 cm | 7.6 km | 300 km |
| Solar System Drive, 2007, Coonabarabran, NSW, Australia | 1:38 000 000 | 37 m | 34 cm | 4.1 km | 205 km |
| Sol Chicago, Chicago, Illinois (Proposed) | 1:73 660 000 | 18.9 m | 17.3 cm | 2.05 km | 61 km (Neptune) |
| University of Maine at Presque Isle | 1:93 000 000 | 15 m | 137 mm | 1.6 km | 64 km |
| Peoria, Illinois | 1:125 000 000 | 11 m | 100 mm | 1.2 km | 47 km |
| Planet Lofoten, Lofoten, Norway (under construction) | 1:200 000 000 | 7m | ? | ? | 30km |
| Boston Museum of Science | 1:400 000 000 | 3.5 m | 32 mm | 375 m | 15.3 km |
| Longview, Lake Sacajawea | 1:?? | 24 inches | 1/4 inch | ? mm | 1.64 miles |
| Somerset Space Walk, Bridgwater and Taunton Canal, UK – one Sun, two sets of planets | 1:530 000 000 | 2.5 m | ? mm | ? m | 11 km |
| York’s solar system model | 1:575 872 239 | 2.417 m | 22.1 mm | 259.73 m | 10.2679 km |
| Nine Views, Zagreb | 1:680 000 000 | 2 m | 1.9 cm | 225 m | 8.7 km |
| Sorghvliet, The Hague | 1:696 000 000 | 2 m | 1.8 cm | 215 m | 6466m (Neptune) |
| McCarthy Observatory, New Milford, CT, USA | 1:761 155 000 | 1.8 m | 16.8 mm | 195 m | 7.07 km |
| Model of the Solar System, Helsinki, Finland | 1:1 000 000 000 | 1.40 m | 12.8 mm | 149.6 m | 6.102 km |
| Planetenmedell Hagen, 1959, Hagen, Germany | 1:1 000 000 000 | 1.39 m | 1.27 cm | 150 m | 5.9 km |
| Zurich, Uetliberg Planetenweg, Switzerland | 1:1 000 000 000 | 1.39 m | 13 mm | 150 m | 5.9 km |
| Saint-Luc, Le Chemin des planètes, Switzerland | 1:1 000 000 000 | 1.39 m | 13 mm | 150 m | 5.9 km |
| Planetenwanderweg, Germany | 1:1 000 000 000 | 1.39 m | 13 mm | 150 m | 5.9 km |
| Hradec Kralove, Czech Republic | 1:1 000 000 000 | 1.39 m | 12.8 mm | 150 m | 5.9 km |
| St. Kilda, Melbourne, Australia | 1:1 000 000 000 | 1.39 m | 12.8 mm | 150 m | 5.9 km |
| Eugene, Oregon[2] | 1:1 000 000 000 | 1.39 m | 12 mm | 150 m | 5.9 km |
| Planet Walk, Munich, Germany | 1:1 290 000 000 | 1.08 m | 9.9 mm | 116 m | 4.57 km |
| Strolling at the speed of light La Malbaie, Québec, Canada | 1:1 500 000 000 | 92.7 cm | 0.85 mm | 100 m | 3 km (Neptune) |
| Solar System Walking Tour, Gainesville, GA, USA | 1:2 000 000 000 | 70 cm | 6 mm | 75 m | 2.9 km |
| Montshire Museum of Science, Norwich, VT, USA | 1:2 200 000 000 | 63 cm | 6 mm | 68 m | 2.7 km |
| Gainesville (FL) Solar Walk | 1:4 000 000 000 | 33.8 cm | 3.2 mm | 37.4 m | 1.479 km |
| The Madison Planet Stroll, 2002, Madison, WI, USA | 1:4 000 000 000 | 35 cm | 3.19 mm | 37 m | 1478 m |
| Otford Solar System Model | 1:4 590 000 000 | 30 cm | 2.7 mm | 32 m | 983 m |
| The Sagan Planet Walk, Ithaca, NY | 1:5 000 000 000 | 27.8 cm | 2.5 mm | 30 m | 1.18 km |
| Delmar Loop Planet Walk, University City, MO | 1:5 000 000 000 | 27.8 cm | 2.5 mm | 30 m | 877 m (Neptune) |
| Jodrell Bank | 1:5 000 000 000? | 30 cm? | 2.5 mm? | 30 m? | 1 km? |
| The Solar Walk, Cleveland, Ohio, USA | 1:5 280 000 000 | 26.4 cm | 2.4 mm | 28.4 m | 1121 m |
| The Thousand-Yard Model | 1:6 336 000 000 | 20.3 cm | 2 mm | 25 m | 983 m |
| Saint-Louis-du-Ha! Ha!, Quebec (ca. 1985) | 1:10 000 000 000 | 13.9 cm | 1.2 mm | 15 m | 590 m |
| Fiske Planetarium, Colorado University, 1987, Boulder, CO, USA | 1:10 000 000 000 | 13.9 cm | 1.2 mm | 15 m | 590 m |
| Voyage, National Mall, 2001, Washington, DC, USA | 1:10 000 000 000 | 13.9 cm | 1.2 mm | 15 m | 590 m |
| Voyage, Power&Light District to Union Station, 2008, Kansas City, Missouri, USA | 1:10 000 000 000 | 13.9 cm | 1.2 mm | 15 m | 590 m |
| Voyage, Space Center Houston, 2008, Houston, Texas, USA | 1:10 000 000 000 | 13.9 cm | 1.2 mm | 15 m | 590 m |
| Voyage, Corpus Christi historic waterfront, 2009, Corpus Christi, Texas, USA | 1:10 000 000 000 | 13.9 cm | 1.2 mm | 15 m | 590 m |
| Voyage, State Capitol Grounds, projected for 2009, Des Moines, Iowa, USA | 1:10 000 000 000 | 13.9 cm | 1.2 mm | 15 m | 590 m |
| Voyage, Inner Harbor, projected for 2010, Baltimore, Maryland, USA | 1:10 000 000 000 | 13.9 cm | 1.2 mm | 15 m | 590 m |
| Le Chemin Solaire, 2011, La Couyère, Brittany, France | 1:22 000 000 000 | 1 m | - | - | - |
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 (3.1 mi) 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:
| Body | Diameter | object comparison | Semi-major axis | scale model location (U.S.) | scale model location (U.K.) | scale model location (Australia) |
|---|---|---|---|---|---|---|
| Sun | 44.6 m (146 ft) | 14 story tall sphere, Spaceship Earth (Epcot) | zero | White House, Washington DC | Buckingham Palace | Sydney Opera House |
| Mercury | 15 cm (6 in) | large grapefruit | 1.9 km (1.2 mi) | National Air and Space Museum | Covent Garden | Elizabeth Bay, New South Wales |
| Venus | 38 cm (15 in) | beach ball | 3.5 km (2.2 mi) | John F. Kennedy Eternal Flame, Arlington National Cemetery | Regent's Park | Sydney Football Stadium |
| Earth | 41 cm (16 in) | classroom globe | 4.8 km (3.0 mi) | Ronald Reagan Washington National Airport | Tower of London | Rozelle Hospital |
| Moon | 10 cm (4 in) | baseball | 12 m (40 ft) from Earth | |||
| Mars | 23 cm (9 in) | dodgeball | 7.2 km (4.5 mi) | Rock Creek Park Golf Course | King's College London | Bondi Beach, New South Wales |
| Ceres | 3 cm (1 in) | golf ball | 13.3 km (8.3 mi) | |||
| Jupiter | 4.55 m (15 ft) | sphere as wide as 5 minivans | 24.9 km (15.5 mi) | George Mason University, Fairfax, Virginia | London Heathrow Airport | Scotland Island, New South Wales |
| Saturn | 3.81 m (12 ft 6 in) | sphere a little taller than a basketball hoop | 45.5 km (28.3 mi) | Marine Corps Base Quantico, Triangle, Virginia | Luton, Bedfordshire | Copacabana, New South Wales |
| Uranus | 1.63 m (5 ft 4 in) | average 8th grade boy | 92.2 km (57.3 mi) | Aberdeen Proving Ground, Aberdeen, Maryland | Waterlooville, Hampshire | Bombo, New South Wales |
| Neptune | 1.55 m (5 ft 1 in) | average 6th grade boy | 144.4 km (89.7 mi) | Newark, Delaware | Calais, France | Nelson Bay, New South Wales |
| Pluto | 7 cm (3 in) | baseball | 190 km (118 mi) | Wildwood, New Jersey | Saint-Valery-sur-Somme, France | Bulahdelah, New South Wales |
| Eris | 8 cm (3 in) | billiard ball | 325 km (202 mi) | Brooklyn, New York | Rotterdam, Netherlands | Port Macquarie, New South Wales |
| α Centauri A | 49.5 m (162 ft) | sphere as wide as 4 school buses | 1,323,500 km (822,400 mi) | over 3 times the distance to the moon | over 3 times the distance to the moon | over 3 times the distance to the moon |
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.
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.
| Body | Diameter | Semi-major axis |
|---|---|---|
| Sun | 0.85 in (21.5 mm) | zero |
| Mercury | 0.003 in (0.08 mm) | 1.0 yd (0.9 m) |
| Venus | 0.007 in (0.19 mm) | 1.9 yd (1.7 m) |
| Earth | 0.008 in (0.20 mm) | 2.5 yd (2.3 m) |
| Mars | 0.004 in (0.10 mm) | 3.8 yd (3.5 m) |
| Ceres | 0.001 in (0.02 mm) | 7.0 yd (6.4 m) |
| Jupiter | 0.085 in (2.16 mm) | 13.1 yd (12.0 m) |
| Saturn | 0.071 in (1.8 mm) | 24.2 yd (22.1 m) |
| Uranus | 0.029 in (0.73 mm) | 48.6 yd (44.4 m) |
| Neptune | 0.028 in (0.7 mm) | 76.1 yd (69.6 m) |
| Pluto | 0.002 in (0.05 mm) | 100.0 yd (91.4 m) |
| Eris | 0.002 in (0.05 mm) | 171.4 yd (156.7 m) |
| α Centauri A | 0.94 in (23.9 mm) | 396 mi (637 km) |
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 "ice cream sprinkles" (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.
| Body | Diameter | Semi-major axis |
|---|---|---|
| Sun | (215 mm) | zero |
| Mercury | (0.8 mm) | (9 m) |
| Venus | (1.9 mm) | (17 m) |
| Earth | (2 mm) | (23 m) |
| Mars | (1 mm) | (35 m) |
| Ceres | (0.2 mm) | (64 m) |
| Jupiter | (21.6 mm) | (120 m) |
| Saturn | (18 mm) | (221 m) |
| Uranus | (7.3 mm) | (444 m) |
| Neptune | (7 mm) | (696 m) |
| Pluto | (0.5 mm) | (914 m) |
| Eris | (0.5 mm) | (1 567 m) |
| α Centauri A | (239 mm) | (6 370 km) |
Children can have some fun with this model, for example Mercury could be a small red sprinkle while Earth might be a larger blue sprinkle. Venus might be smaller. Children can look for two small red sprinkles 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.
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.
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