The Sagan Planet Walk is a walkable scale model of the solar system, located in Ithaca, New York. The model scales the entire solar system--both planet size and distances between them--down to one five billionth of its actual size. Consisting of 11 obelisks situated along a 1.18-kilometre (0.73-mile) path through the streets of downtown Ithaca, the Planet Walk leads from the sun at Center Ithaca to Pluto at the Ithaca Sciencenter.
The scaled size of the sun is given by a 27.8-centimetre (10.9-inch) diameter circular frame repeated at the top of each 6-foot (1.8-metre) tall obelisk. Centered within each sun-sized frame, the proportional size of each planet is represented by a small sphere affixed in a glass window.
The exhibition was originally created in 1997 in memory of Ithaca resident and Cornell Professor Carl Sagan. In 2012, the model was expanded 5,000 miles to include a representation of the sun's closest neighboring star--[Alpha Centauri]]--at the ‘Imiloa Astronomy Center at the University of Hawaii.
The Sun and Inner Planets
The obelisk for the Sun is located in the center of the Ithaca Commons. The obelisks for the four inner planets are all close by, and within eyesight of the Sun, contained within the commons area stretching north towards Seneca Street. The representations of each planet appear quite small within their glass windows, and can even be somewhat hard to see. Once leaving the inner planets, a visitor to the Planet Walk should turn west along Seneca Street to continue towards Jupiter.
The Asteroid Belt
The obelisk representing the asteroid belt bewteen the inner planets and Jupiter was added several years after the initial installation. It's display contains the only public, unguarded meteorite in the world.
Jupiter's obelisk sits outside the downtown Dewitt Mall, not far from the Moosewood Restaurant. The model of Jupiter within the glass window is the first planet model easily visible from a distance. To reach Saturn, visitors should turn north along Cayuga street.
At the corner of Cayuga and Court street, Saturn's obelisk sits outside the former location of the Tompkins County Public Library. Since the original installation of the Planet Walk, the library has moved to a new location, leaving Saturn no longer attached to a local landmark. Visitors continue northward along Cayuga street towards Uranus.
Just across Cascadilla Creek at the entrance to Thompson Park is the obelisk for Uranus.
Neptune and the Carl Sagan Bridge
From Uranus, visitors must follow Willow Avenue northwest and cross the Carl Sagan bridge at Adams street to reach Neptune. The Carl Sagan bridge was built in 2000, and features nine circular windows adorned with the signs of the nine planets. The obelisk for Neptune is located just across the bridge in Conley Park.
Pluto and the Ithaca Sciencenter
As the Planet Walk was conceived and built prior to Pluto losing its planetary status in 2006, the model includes an obelisk for Pluto as well as the eight official planets. Pluto's obelisk is located just outside the Ithaca Sciencenter on First street.
Television host and former student of Carl Sagan, Bill Nye, has narrated a podcast tour of the Planet Walk which can be accessed free by calling 703.637.6237 as you walk through the solar system.
The models of the Solar System, in order: