In this, the International Year of Astronomy, there may be no better way to explore our solar system than by bicycle.

It’s just a little more than 23 miles to Pluto, which is in a marsh near Mount Horeb. Neptune is between Verona and Riley, so you can plan a stop at the Riley Tavern to toast your departure from the realm of the inner planets.

Welcome to what its originators are calling one of “the largest scale models of our solar system in the universe.”

Through October, it is possible to travel along Madison and Dane County bike trails from the sun, at Monona Terrace, to the outer reaches of the solar system in Mount Horeb, reading informative signs at the location of each planet.

The project is called Planet Trek Dane County.

Jim Lattis, a UW-Madison astronomer and director of UW Space Place, said the project may be one of his all-time favorite outreach efforts.

The idea was hatched last year to mark the International Year of Astronomy, which is being observed around the world in 2009.

Having worked on smaller scale models, Lattis said he was hoping to create a model large enough that, even at its scaled-down size, tiny Pluto would be the size of a marble.

The idea, Lattis explained, was to line up the planets of our solar system along some kind of path that would give people a chance to travel from planet to planet and get an accurate idea of the distances between their orbits.

Generally, distances in space are so vast that they are nearly impossible to comprehend. A combination of Madison and Dane County bike trails — the Southwest Commuter Trail and the Military Ridge Trail — proved to offer the best setting for the miniature solar system.

After some calculating and experimenting with different scales, Lattis got on his bike one day last summer, set his hand-held GPS unit to zero, and pedalled off to find Pluto.

Lattis had placed the sun near Monona Terrace.

The model would be based on a scale of 200 million to one, meaning planets and the distances between them would have to be shrunk by a factor of 200 million.

This would downsize the sun, for example, to a sphere 24 feet in diameter. Earth would be an apple. All together, the walker/bicyclist/space explorer has to make 11 stops along the route — not including the above-mentioned sortie into the Riley Tavern.

For example, after leaving the sun on the Southwest Commuter Bike Trail and heading West, you’ll come across Venus 0.35 miles later.

Earth is near the Brittingham Boathouse, 0.48 miles from the sun.

Colorful signs offer a wealth of information about each planet, including its scaled-down size.

In accord with the latest science, Pluto is described as a dwarf planet rather than a full-fledged planet. And, to be fair, another dwarf planet, Ceres, is also included. You’ll find it just past Mills Street, about 1.35 miles from the sun.

Lattis hopes that travelers will take time to have some fun with the model. You can, for example, practice traveling at the speed of light. If you walk along at a moderate pace through the solar system, about 3.5 miles per hour, you’ll be trucking along at the scaled speed of light.

At that pace, after leaving the sun, it should take you about eight minutes to travel to earth (if you don’t get stopped by the single traffic light), just as it takes light eight minutes to travel from the sun to the earth. What else to know before you start on your journey?

Oh yes, if you pass beyond Saturn and the inner planets, you’ll need a trail pass from the state Department of Natural Resources which, apparently, has found a way to regulate travel in outer space.

The passes can be purchased at kiosks placed conveniently throughout the outer solar system, which we know as the Military Ridge Trail.