visitors to the Voyage exhibition are unaware of
the level of accuracy of this model Solar System. For those
readers with a deeper understanding of apparent motions in
Earth’s sky, here is the rest of the Voyage.
The model planets and moons are created through 3-dimensional
laser sculpting inside solid crystal. The technique uses
a laser to precisely focus energy at a specific location inside
a clear slab of glass. The result is an extremely small spherical
fracture at the point of focus. Each fracture is a pixel—a
‘picture element’ akin to the pixels that make
up a 2-dimensional digital image. But in this case, the computer-guided
laser can create 3-dimensional structures of significant complexity,
fully inside the glass slab, and constructed one pixel at
a time. Visit www.crystalimpressions.com.
We therefore had the ability to create spherical
model planets and moons of highly accurate size; place moons
in their appropriate orbital planes and at the correct distances
from their parent planet; and reproduce the ring systems of
giant planets Jupiter, Saturn, Uranus, and Neptune, including
accurate ring width and position of ring divisions. In the
case of Jupiter and Saturn, their equatorial diameters are
noticeably greater than their pole-to-pole diameters and this
‘oblateness’ could also be accurately portrayed
through laser sculpting.
For a given planet, its shape, ring system, and orbits of
moons, are all structures that are oriented in a well-defined
manner relative to the planet’s equatorial plane and
spin axis. All these data would be provided to the computer
driving the laser. But one still needs to correctly orient
the planet’s spin axis in space, relative to the spin
axes of the other planets, if you’re truly going to
create a model of the Solar System. We wanted the Voyage
model Solar System to provide an experience as close as possible
to visitor as cosmic giant wandering through the real
But how were we going to define the orientation of the planetary
spin axes relative to each other?
observers see themselves at the center of a spherical canopy
of stars, called the celestial sphere. Astronomers
project Earth’s latitude and longitude onto the celestial
sphere to create a grid that can be used to precisely define
the position of an object in the sky. It is also true that
every planet’s spin axis, if infinitely extended, will
intersect this grid at two well-defined points. In other words,
every planet’s spin axis is oriented relative to the
To realize the vision for Voyage, we imagined a
model celestial sphere centered on the model Earth. Defining
the orientation of the model celestial sphere relative to
the National Mall is all that’s needed to correctly
orient all planetary spin axes. The model planets would then
be portrayed with accurate orientations in space, which would
be visible to the visitor through the orientation of the model
ring systems, planetary oblateness, and moons in the glass.
The solution was to first adopt the horizontal plane of the
National Mall as the plane of the Earth’s orbit around
the Sun, known as the ecliptic plane. The Earth spins
on an axis that is tipped 66.5 degrees to that plane (tipped
23.5 degrees from vertical). The spin axis maintains a fixed
orientation in space as Earth orbits the Sun. This is the
case for all the planets, though the orientation in space
of each spin axis is different.
To fully define the model celestial sphere, given that the
plane of the Mall is the ecliptic, one only needs to specify
that the model Earth’s location represents a particular
time in its orbit around the model Sun. The moment in time
that is chosen is the date of the Vernal Equinox, near March
The reason for the choice derives from the orientation of
the National Mall. The exhibition is placed along Jefferson
Drive, which runs precisely east-west. The model Earth is
located 15 meters due west of the model Sun. At the time of
the Vernal Equinox near March 21, when standing at the model
Earth, the real Sun rises due east—directly behind the
model Sun, and both Suns appear to be the same angular size.
The positions of the model Earth and Sun therefore reflect
the time of the Vernal Equinox, the orientation of the celestial
sphere is fixed, and the planetary ring systems, planetary
oblateness, and position of moons can all be accurately portrayed.
The sizes, orientations, and oblateness associated with
the Voyage model planets are shown in the illustration.
You see crystalline, 3-D versions of these images, together
with moons where appropriate, when looking through the glass
of the Voyage planetary Units.
The only significant liberty taken in the
Voyage exhibition is that the other planets are also
placed along the Earth-Sun line, so the visitor can get an
accurate understanding of the relative distances of the planets
from the Sun. But the planets never line up, which
is stated on every storyboard.
A computer model of the Solar System was developed to test
the assumption that the planets are never aligned. In the
computer model, planets were initially placed in their orbits
at random locations, the clock was started, and the planets
proceeded to orbit the Sun. Over the course of four billion
years, the planets were never seen to line up in any reasonable
interpretation of ‘aligned’.