Connecting the Earth & Sky: The Armillary Sphere in the Evans Center

Artist and Scientist Leonardo Da Vinci said, “To develop a complete mind, study the science of art, study the art of science, learn how to see. Realize that everything connects to everything else”. The Edward P. Evans Academic Center at Eaglebrook School was constructed as a space to hold science, art, and music classes. There is a dome at the top of the curved stairway, build to mimic a Nautilus shell, that has been empty save the skylight since the building opened.

There were plans for that spot, however. Local artist Charles Wiemeyer, the father of current student Henry ’19, was commissioned to build an armillary sphere for the space, and that sculpture was completed over the recent March Break, almost a year after the Evans Center opening. David Spence, principal at Windigo Architecture & Design, who designed the Evans Center from the early stages of the project, felt that an armillary sphere would be the perfect complement to a building designed to foster creativity and discovery. “If there is one place an observer would understand DaVinci’s point, standing under the armillary would be the place,” he said. “As part of the building’s purpose to educate students, the sculptural armillary is meant to inspire contemplation about one’s connection with the planet and universe. The student ascending the stair and the shadows tracing the rings of the armillary all play into the ‘feeling’ of the earth’s spin and orbit around the sun. The stair creates movement of the body; the armillary shows movement of the place. The tree of life is also set into the composition by showing humans’ place amongst the planet’s organisms. The vertical stratification of these three scientific themes reflect how we view the world, from the ground, through the air and up into the sky. The intent though was to not just offer a science lesson but also create an “art-chitectural” expression within the building,” he continued.

What, exactly, is an Armillary Sphere? There are general principles of a sphere, but each one is a bit different. An armillary sphere is a model of the celestial sphere, centered either on the Earth or the Sun.  The Eaglebrook armillary is an Earth-centered, or Ptolemaic, armillary. A typical armillary used for observation is adjustable based on the date.  Our armillary is fixed at a typical summer noon when the sun is high in the sky.

The flat, vertical ring with the crescent removed is the meridian ring, identifying the local meridian, or midpoint of the sun’s daily path. This means it is oriented to geographical north and south. Its zero-degree mark is on the horizon and the 90-degree mark directly overhead.

The band at the wall is the horizon ring, marking north at zero and proceeding clockwise around the horizon. This and the meridian ring combine to locate the azimuth and altitude of objects in the sky. It also has a pointer marking magnetic north, which at Eaglebrook is about 14 degrees west of geographic north.

The next set of objects identifies the tilt and orientation of the Earth’s axis. The central tube points to Polaris, the North Star, and its angle of approximately 42.5 degrees marks Eaglebrook’s latitude. The small ring near its top marks the precession of the equinoxes, or the track through which the Earth’s the North Pole wobbles over a 26,000-year cycle. The wider band perpendicular to the central tube marks the Earth’s, and the celestial, equator. It is set to the local longitude, 72.6 degrees west, or 287.4 degrees east of the global meridian in Greenwich, England. The inside of this band marks the approximate time zones – noon at Eaglebrook, later in the day to the east and earlier in the day to the west. Finally, the two tropics are shown by the two blue pipes, the Tropic of Cancer in the northern hemisphere and the Tropic of Capricorn in the southern hemisphere. These are the latitudes where the sun is directly overhead at the summer and winter solstices, respectively.

The large band with the turquoise stripe marks the ecliptic, which is the annual apparent path of the sun in the sky. The sun appears to move like this because of the tilt of the Earth’s axis relative to the plane of its orbit around the sun.  Most of the planets of the solar system are on or near this same plane, meaning that they too appear to move along this band during the year. The constellations along the ecliptic, the zodiac, were key regions of the sky in ancient astronomy for predicting the seasons. At the ancient midsummer solstice in the northern hemisphere, the sun was just rising in the constellation Cancer at dawn – hence the name “Tropic of Cancer”. In the several thousand years since, precession has meant that the apparent position of the sun relative to the zodiac has shifted, and midsummer now occurs in Gemini. But the older names persist. Eaglebrook’s armillary locates the zodiac constellations near the tropics that bear their names.

Last but not least, the constellation Aquila, the Eagle, is represented. Although enlarged relative to its actual scale in the armillary, it is in its correct position just north of the celestial equator near Sagittarius. Altair, the principal star in Aquila at the head of the eagle, is part of the “Summer Triangle” with the stars Vega and Deneb. Since it is in the summer sky in the evening, it is below the horizon during the early part of the summer day as it appears here. Look for Aquila after sunset from July through September.

Charles had his son Henry help with the installation of the sculpture during what was already Henry’s break time. Take a look at photos of the sphere here, and be sure to check it out the next time you are at the Evans Center.