The Sciencenter's 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 eleven obelisks situated along
a 1.18 km (0.73 mi) path through the streets
of downtown Ithaca, the Planet Walk leads
from the Sun at Center Ithaca to Pluto at
the Ithaca Sciencenter.
The exhibition was originally created in 1997
in memory of Ithaca resident and Cornell Professor
Carl Sagan.
In 2012, the model was expanded 7,630 kilometers
(4,740 mi) to include a representation of
Alpha Centauri, the Sun's closest neighboring
star, at the ‘Imiloa Astronomy Center at
the University of Hawaii.
The addition of the Alpha Centauri Obelisk
made it the world's largest exhibition.In
2014, the inner planets and Sun were removed
as part of extensive construction being done
to the Ithaca Commons, but have since been
replaced.
In 2015, a grant was approved to further expand
the exhibition by installing an exoplanet
Kepler-37d station on the Moon 384,500 kilometers
(238,900 mi) away.
== Individual models ==
The scaled size of the Sun is given by a 27.8
cm (10.9 in) diameter circular frame repeated
at the top of each 6 ft (1.8 m) 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.
All of the original planet locations were
chosen not only for accuracy to scale but
also to highlight local landmarks and public
spaces within Ithaca.
However, since the original installation of
the Planet Walk the public library has moved
to a new location, leaving Saturn no longer
attached to a local landmark.
Additionally, as of 2016-2017, the original
planets in plexiglass at each station have
been replaced by simple yellow disks with
the planet simply represented by a relatively-sized
hole.
Some attendant moons are now represented by
tiny holes in the disks.
=== The Sun ===
The Sun Obelisk is located in the center of
the Ithaca Commons, a pedestrian shopping
area in the heart of downtown Ithaca.
The round window representing the size of
the Sun at this station is roughly the size
of a basketball and, in this obelisk only,
contains no glass.
All the subsequent obelisks in the Solar System
model have Sun-sized glass windows containing
their respective planets for the sake of comparison.
=== The Inner Planets ===
The obelisks for the four inner planets are
all contained within the commons area stretching
north towards Seneca Street.
Mercury is situated to scale about 12.7 yards
(11.6 meters) away from the Sun, Venus another
10 yards (9.1 meters) away, Earth another
9.3 yards (8.5 meters) away, and Mars another
17.1 yards (15.6 meters) away.
This keeps the four inner planets within eyesight
of the Sun, yet the representations of each
planet appear quite small within their glass
windows, and can even be somewhat hard to
see.
The contrast between the size of the Sun and
the size of the inner planets coupled with
the visible distance between them illustrate
the vastness and emptiness of space.
=== The Asteroid Belt ===
Once leaving the inner planets, a visitor
to the Planet Walk turns west along Seneca
Street to continue towards Jupiter.
Between Mars and Jupiter lies the asteroid
belt.
The obelisk representing the asteroid belt
was added several years after the initial
installation.
Its display contains the only public, unguarded
meteorite in the world.
=== Jupiter ===
The Jupiter Obelisk sits at the corner of
Seneca and Cayuga streets, outside the downtown
Dewitt Mall, and not far from the famed Moosewood
Restaurant.
The model of Jupiter within the glass window
is the first planet representation on the
walk that is easily visible, demonstrating
how much bigger than the inner planets it
is.
=== Saturn ===
To reach the Saturn Obelisk, visitors turn
north and continue 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.
The rings of Saturn are clearly visible within
the circular window.
=== Uranus ===
Visitors continue northward along Cayuga street
from Saturn, reaching the obelisk for Uranus
just across Cascadilla Creek at the entrance
to Thompson Park.
=== Neptune and the Carl Sagan Bridge ===
From Uranus, visitors follow Willow Avenue
northwest and cross the Carl Sagan bridge
at Adams street to reach the Neptune Obelisk.
The Carl Sagan Bridge, built in 2000, 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 Sciencenter ===
The Planet Walk was conceived and built prior
to Pluto losing its planetary status in 2006,
and the model includes the Pluto Obelisk,
which is located just outside the Sciencenter
on First street.
=== Alpha Centauri ===
The model was expanded 7,630 kilometers (4,740
mi) in 2012 to include Alpha Centauri, the
star closest to the Sun.
The Alpha Centauri Obelisk is exhibited at
the ‘‘Imiloa Astronomy Center of Hawai‘i
at the University of Hawaii in Hilo, Hawaii.
This extension made the Sagan Planet Walk
the world's largest exhibition.
== Bill Nye ==
Television host and former student of Carl
Sagan, Bill Nye, narrated a podcast tour of
the Planet Walk in 2006 which can be accessed
free by calling 703.637.6237 as you walk through
the scale-model representation of the Solar
System.
== Table of Scaled Sizes and Distances ==
== History and Timetable of expansions ==
1997 Original Planet Walk created in Ithaca,
with ten obelisks for the Sun and nine planets
2000 Carl Sagan Bridge built across Cascadilla
Creek on the way to the Neptune Obelisk
2006 Audio Tour narrated by Bill Nye added
2009 Asteroid Belt Obelisk added between the
inner and outer planets
2009 Newly designed Passport to the Solar
System
2012 Station depicting Alpha Centauri erected
in Hawaii
Kepler-37d station to be installed on Moon
(installation date TBD)
== Model gallery ==
The models of the Solar System, in order:
== Models inspired by the Sagan Planet Walk
==
The Sagan Planet Walk has inspired the creation
of other scale-model Solar Systems in the
United States.
The Delmar Loop Planet Walk in St. Louis,
Missouri:"In 2006, I became aware of the Sagan
Planet Walk in Ithaca, NY, and as an amateur
astronomy buff, I found the idea of a scale
model solar system to be a fascinating concept.
While researching other such models on the
Internet, I developed the idea to build one
in St. Louis."—Stephen WalkerThe Anchorage
Light Speed Planet Walk in Alaska:"The idea
for this project was ignited by [Eli Menaker's]
visit to the Carl Sagan Memorial Planet Walk
in Ithaca, New York."
== 
See also ==
Solar System model
