Finally, the Atwood Sphere

I might be 46 and prone to the middle-aged illusion that I've fully acquainted myself with the world, and it might take effort to resist the feeling that I know everything I need to know, and that the world is now just one damn thing after another till check-out time. But fortunately, I still see things that remind me that the marvels of the world, natural and manmade, are inexhaustible; I'm the exhaustible one. Such as this manmade-item.

There's surprisingly little on the web about the Atwood Sphere: one of those increasingly rare creatures that has no Wikipedia entry of its own, though it would certainly qualify for one. This is all that the Adler web site itself says: "Atwood Sphere, Chicago's oldest planetarium, was constructed in 1913. The sphere is 15 feet in diameter with 692 holes drilled through its metal surface, allowing light to enter and show the positions of the brightest stars in the night sky. School groups may not participate in presentations made inside the Atwood Sphere due to capacity limitations. However, museum services staff provide ongoing presentations about the Atwood Sphere in the gallery."

Indeed, there's no room inside for a whole school group, though you could cram about 10 kids inside. I was inside with five other adults and one child (Lilly). It was an unexpected treat. After the medicore planetarium show, Lilly and I were taking in some of the exhibits when we turned a corner and came face-to-face, if it had a face, with an enormous steel ball mounted in its own alcove. The steel was wash-tub gray. On one side at the bottom was a hatch large enough to allow a small car, like a mining car or a special elevator for the handicapped, to enter the sphere via a small, diagonal set of tracks. Visitors entered the car -- a maximum of eight, the sign said -- and an operator pushed a button that took the car into the sphere.

Once inside, the hatch closed most of the way, so that it was dark in there, except that you could see the pinpoints of light that represented stars. The brighter stars had bigger holes. Some, but not all, of the constellations were drawn in a luminous ink. According to the guide, there were once small holes that could be opened and closed to represent planets at various positions, but they were gone. An electric motor turned the sphere while you sat in the car watching, to similar the sky as the Earth rotates. I can't say it was an absolutely realistic depiction of the sky, but it was a fine simulation, and in 1913 there were no Zeiss planetariums. According to nearby signs, the Atwood was very popular until the Adler itself opened with a Zeiss in 1930, a new marvel. During WWII, the sphere was used to teach pilots about celestial navigation, and later was painted to look like an Earth globe. Presumably people weren't going inside during the last decades of the 20th century.

The web site of the Maynard F. Jordan Planetarium gives a little context: "A breakthrough in three-dimensional representations of the sky came in 1664 with the construction of devices such as the Gottorp Globe. This was a hollow sphere, 10 feet (3 meters) in diameter, inside which images of the constellations and gilded stars were placed. Accommodating up to 10 people inside, this globe could rotate and thus demonstrate the daily motion of the constellations. In 1758, Charles Long improved on this idea by building a rotatable sphere 18 feet (5.5 meters) in diameter, accommodating 30 persons. Instead of painted constellations, Long's sphere, called the "Uranium" ("place of the heavens"), had tiny holes through which light from outside could shine, making it look to viewers inside as if they were actually looking at stars in the dark.

"A similar rotatable sphere, built by Charles Atwood in 1913, was until recently on permanent display at the Chicago Academy of Sciences. Called the Atwood Sphere - and later re-christened the Globe Planetarium - it was the first sky simulator of any kind in the United States."

The Adler acquired the Atwood less than 10 years ago, and restored it, more or less, to its original state. Is that not cool? Going inside a ball made of wash-tub steel while it rotates and you see stars?