Outdoors Blog

Greenbelt’s little-known Planet Walk shows solar system’s scale

A series of bollards along the Greenbelt and in Julia Davis Park present information about the planets, forming the Planet Walk. Neptune is between the Greenbelt and the Boise River.
A series of bollards along the Greenbelt and in Julia Davis Park present information about the planets, forming the Planet Walk. Neptune is between the Greenbelt and the Boise River. ccripe@idahostatesman.com

Even if you’ve walked, run, skated, biked or otherwise traveled the Boise River Greenbelt a hundred times, you might not know about Planet Walk — an educational ode to the solar system that was installed more than two decades ago.

“If you’re not sure where to look for them, they’re easy to skip,” said Woody Sobey, the former education director at the Discovery Center of Idaho. “I would suspect that maybe 1 percent of the people who use the Greenbelt know about the Planet Walk.”

All of the bollards with details about the planets are still there — even Pluto, which has become a source of some astronomical controversy. There’s even an app (DCI Planets) to help you navigate Boise’s solar system.

The Discovery Center is about to make an improvement that might put a little more of a spotlight on Planet Walk. The sun, formerly in the lobby of the building at 131 Myrtle Street, is moving outside the entrance as part of a new display.

The bollards are distributed in a line from the sun at distances roughly to scale with where they would be if all of the planets were in a line. The plaques include a scaled representation of the planet — based on its size relative to the sun at the Discovery Center. The plaques also list the size of the planet (75,000-mile diameter for Saturn), the distance from the sun (885 million miles), the length of its year (29 Earth years) and its mass (95 Earths).

The last line tells the distance from the model sun (1,705 feet).

A map shows the location of the bollards.

Mercury is only 69 feet from the model sun. Venus is just on the other side of the Discovery Bridge that crosses from the parking lot to the park. Pluto is 7,054 feet from the sun — near Idaho Fallen Firefighter Memorial Park. The round-trip walk is nearly 3 miles.

The nearest visible star would be at the South Pole on this scale, according to the Discovery Center.

Planet Walk’s ability to demonstrate the distance between planets is one of its best features, Sobey said.

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