Planets Along the Promenade
1The coastal town of Port Alder spent two years raising and strengthening its seawall so that winter storm waves would not flood the harbor streets. The new wall has a wide, straight promenade on top that runs 500 m from the ferry dock to the lighthouse. When the town asked for ideas to make the walk more interesting, the Port Alder Middle School science club proposed a scale model of the solar system.
2Eighth grader Wren Takahashi and the town planner, Mr. Elio Fontaine, started with the data in the table. The Sun would be a bronze disk set into the walk at the ferry dock. Each planet would get a marker post at its scaled distance from the Sun. Every post would carry a plaque with the planet's real diameter, its real distance from the Sun and one fact about its surface, so the walk would teach visitors even when the weather was gray.
3For distances the club chose the scale 1 m = 10 million km. At first Wren wanted to use the same scale for the size of each planet and the Sun. Then she worked out that at that scale the Sun's disk would be smaller than a dinner plate, and Earth would be a dot smaller than a grain of rice. Visitors would walk right past it.
4The club settled on two scales. Distances along the promenade use 1 m = 10 million km. Each marker post holds a model planet built at a second scale, 1 cm = 1,000 km, so Earth's model is a ball about 12.8 cm across. A sign at every post reminds visitors that the planet and its distance are shown at different scales. The bronze Sun disk only marks the starting point and is not built to either scale.
5Mr. Fontaine also asked about Pluto, a dwarf planet. Its average distance from the Sun is about 5,900 million km. Wren checked a walking pace of about 1.4 m each second and found that a visitor could walk from the Sun disk to the Neptune post in about five or six minutes.