A sense of scale

How far is the nearest star?

The closest star beyond the Sun is Proxima Centauri, about 4.25 light-years away. If the Sun were a 6.7 cm tennis ball, Proxima would still be about 1,933 kilometers away.

That is why a scale model of the solar system can fit into a park, while a model that reaches the next star needs a much bigger map. The empty space between stars is a large part of what makes the universe difficult to picture.

What does 4.25 light-years actually mean?

A light-year is a unit of distance: how far light travels in a year. One light-year is approximately 9.46 trillion km. Proxima's distance is therefore about 40.2 trillion km. When we observe Proxima, we see light that left it more than four years ago.

Proxima is a red dwarf in the Alpha Centauri system. Its brighter neighbors, Alpha Centauri A and B, are a little farther away. The Sun itself is our nearest star; in this model it is the zero point, so “nearest star” means the nearest star beyond the Sun.

How the tennis-ball Sun calculation works

The model reduces both the Sun and the distances by the same factor. It uses a solar diameter of 1,392,700 km and a tennis-ball diameter of 0.000067 km, or 6.7 cm. This makes the model about 20.8 billion times smaller than the original.

Model distance = real distance × model Sun diameter ÷ real Sun diameter

With those inputs, one light-year becomes about 455.14 km. Multiply that by the catalog value of 4.2465 light-years for Proxima and the result is 1,932.74 km, rounded to 1,933 km.

For another reference, Earth would orbit the tennis-ball Sun at about 7.2 meters. The gap from the Sun to Proxima would be roughly 269,000 times that Earth-Sun distance. A familiar-looking solar system can still have an astonishingly distant next-door neighbor.

What if the Sun were even smaller?

A smaller model Sun reduces every distance with it. The app uses one representative size for each everyday object; an actual grain of sand or human hair can vary.

Why put the stars on an Earth map?

A map connects an abstract number to a recognizable place. The model can start at your location, so you can compare a stellar distance with a journey across a region or continent. You can also use the default preview without sharing your location.

The directions are an illustration based on galactic coordinates, rather than a local sky chart. Three-dimensional space is simplified onto a flat map, and the lines represent scaled distances, not driving routes. Brightness, stellar size, and travel time are separate questions.

For much larger distances, read how an atom-sized Sun changes the scale of the observable universe.