The dome of the Wenus planetarium is about fourteen metres across. If it were the Sun, the Earth would be a grapefruit a kilometre and a half away — somewhere in Jędrzychów. Jupiter, as wide as a pair of outstretched arms, would stand in the park in Kiełpin.
Models of the Solar System nearly always cheat, and in one of two ways. Either the planets sit side by side at a decent size and the distances are invented, or the distances are stretched and the planets become dots that cannot show you that Jupiter is a thousand times the Earth.
Here there is one scale. The same number shrinks the Sun’s diameter and the road to Neptune — which is why this model does not fit in a park but in a city, and why walking it feels the way crossing the Solar System really is: long, and mostly empty.
The Sun is already built. The dome on the roof of the Kepler Science Centre is a sphere of roughly the right shape in the right place, in the middle of town. The rest is ten plaques and a few walks.
Fourteen metres is the dome. But the size is not settled: the smaller the Sun, the more of the system fits inside the city — and the smaller the planets get, down to beads nobody would notice. The slider is here so that the trade can be seen before it is made.
Scale 1 : 100,000,000
A plaque can stand inside the city — out to Jupiter. The whole orbit, whichever way you walk — out to Mars.
To reach further, the Sun has to shrink — tap to see it:
| Body | Diameter | From the Sun | Closest – furthest | City |
|---|---|---|---|---|
| Sunthe planetarium dome | 14 m | — | — | — |
| Mercury | 4.9 cm | 582 m | 462 m – 702 m | whole orbit |
| Venus | 12.2 cm | 1,088 m | 1,080 m – 1,095 m | whole orbit |
| EarthMoon 3.5 cm, 3.86 m from Earth | 12.8 cm | 1,504 m | 1,479 m – 1,529 m | whole orbit |
| Mars | 6.8 cm | 2,292 m | 2,077 m – 2,506 m | whole orbit |
| Jupiter | 1.41 m | 7,826 m | 7,445 m – 8,206 m | part of it |
| Saturnrings 2.73 m | 1.17 m | 14.4 km | 13.6 km – 15.1 km | outside |
| Uranus | 51 cm | 28.8 km | 27.5 km – 30.2 km | outside |
| Neptune | 49.5 cm | 45.4 km | 44.9 km – 45.8 km | outside |
Voyager 1, on its way since 1977 and still transmitting, would be 259 km from here.
Proxima Centauri, the nearest star, would stand 403,856 km away — further than the Moon really is.
One version of this goes to the city’s participatory budget — the one with the dome as the Sun. The plaques need not stand exactly on the mean orbit, because the planets do not either: each travels between its perihelion and its aphelion, a band from a dozen metres wide (Venus) to nearly three kilometres (Uranus). A place is good if it falls inside that band — if it stands at a distance the planet really reaches.
The places proposed are grounds rather than points, so a plaque goes where the orbit crosses them. Park Tysiąclecia runs from 641 to 1333 metres out, which puts Venus’s whole band inside it; the park in Kiełpin reaches from 7418 to 7609 metres and crosses into Jupiter’s.
The six places inside the city are also, every one of them, city land — without that the project could not enter the participatory budget at all, since it funds building work only on ground the city owns. Nothing here has yet been agreed with the people who manage those grounds.
| Body | Model diameter | Orbit from the dome | Proposed place |
|---|---|---|---|
| Mercury | 4.9 cm | 582 m | Park WinnyAlso considered: Palmiarnia, Filharmonia Zielonogórska |
| Venus | 12.2 cm | 1,088 m | Park TysiącleciaAlso considered: Centrum Przyrodnicze |
| Earththe Moon 3.5 cm on a plaque of its own, 3.86 m away | 12.8 cm | 1,504 m | Zielony PrzystanekAlso considered: Wieża Braniborska, Amfiteatr |
| Mars | 6.8 cm | 2,292 m | Park Braci GierymskichAlso considered: CRS |
| Jupiter | 1.41 m | 7,826 m | Park w KiełpinieAlso considered: Nowy Kisielin, Zawada |
| Saturn | 1.17 m | 14.4 km | ZabórAlso considered: Drzonów |
| Uranus | 51 cm | 28.8 km | KargowaAlso considered: Babimost, Krosno Odrzańskie |
| Neptune | 49.5 cm | 45.4 km | Wolsztyn |
Distances you have to walk. A planetarium shows the sky in a room; this model shows it in the streets, and does the one thing a screen cannot. A child who walks the kilometre and a half from the dome to the Earth, and then reads that Jupiter is five times further still, knows something about the Solar System that no illustration conveys — because every illustration lies to fit the page. At the Earth’s plaque one more thing lands: the Moon is not “right next to us”. Beside a grapefruit the size of our planet it stands almost four metres away — and if it happened to be at its furthest, all eight planets would fit end to end in that gap. For a school it is a ready-made lesson outdoors: there is a route, there are numbers on the plaques, and nothing to prepare or book.
One walk. From the dome to Jupiter in Kiełpin is 7.5 kilometres due south — a day on foot, an hour by bike, past Park Winny, Park Tysiąclecia and Jędrzychów. The plaques stand where something already is, so the route leads nowhere new: it ties together what the city already has. Models like this work elsewhere — the best known, in Sweden, uses an arena in Stockholm for its Sun and reaches hundreds of kilometres north, and people travel to collect the planets.
A second stage that leaves town by itself. Saturn falls in the commune of Zabór, Uranus near Kargowa, Neptune in Wolsztyn — each of those gets a reason to join something that started in Zielona Góra, and a point of its own on the same map. The city pays for nothing beyond its border and is the centre of the system all the same.
A post with a plate and a sphere at the model’s true scale — from the Moon’s three and a half centimetres to Jupiter’s metre forty. On the plate: the body’s name, its real diameter, its real distance from the Sun, the distance and bearing back to the dome, and a QR code to a map of the whole model. Where that map lives is open — it belongs with the city or the planetarium rather than with us; if that is easier, we will host and maintain it, as we do this page. The smaller spheres are set into the plate and read with a finger; Jupiter and Saturn stand as spheres of their own, being at this scale wider than a person.
The first fits inside the city. A plaque at the dome, which explains the whole thing and is the model’s zero point, and six more: Mercury, Venus, the Earth, the Moon, Mars and Jupiter. The furthest — Jupiter — stands 7.5 kilometres from the dome, in the park in Kiełpin, still within Zielona Góra. That is the scope of the application.
The second needs the neighbours. Saturn falls in the commune of Zabór, Uranus near Kargowa or at the Babimost airport, and Neptune in Wolsztyn, already in another voivodeship. The city cannot fund them, as they lie beyond its border. Until there are conversations with those communes, the three exist where they are now: on the map above.
The figures go here once there is a quotation. For a participatory budget what matters as much is what is not on that list: once installed, the model needs no running. There is nothing in it to switch on, power, service or update — the planets will not move themselves, and the distances between them will not change for the next few billion years.
This is a proposal, not a decision of the city, and the size of the Sun is still open — the slider above exists so that the choice can be calculated rather than felt.