June 13, 2003

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June 13, 2003: Four hundred years ago the makeup of our solar system was a matter of intense debate. Was Earth at the center of everything? Or the Sun? Astronomers knew of six planets including our own. Why six? And what determined their spacing? No one knew.

In 1595, Johannes Kepler had a beautiful idea. He was fascinated by the five "perfect solids," also known as Platonic solids: the tetrahedron, the cube, the octahedron, the dodecahedron and the icosahedron (pictured right). Each is made of only one kind of regular polygon--a triangle, a square or a pentagon--hence their "perfection." Kepler realized that these five solids nestled one inside another defined the supporting structures for six circular orbits. Planetary orbits! "The intense pleasure I have received from this discovery can never be told in words," wrote Kepler.

Too bad it was wrong. Planetary orbits are not circular--a fact later discovered by Kepler himself. Now we know there are nine planets, not six, and the Platonic solids have nothing to do with the architecture of our solar system.

Nevertheless, 3D solids made of squares and triangles and pentagons continue to fascinate scientists and explorers. Witness today's picture: a hebesphenomegacorona onboard the International Space Station.

This solid has 21 faces, three squares and 18 triangles. It is one of the three-dimensional shapes called "Johnson solids" you can make by mixing different kinds of regular polygons. In 1969, mathematician Viktor Zalgaller proved there were only 92 Johnson solids, and he gave each one a fanciful name: e.g., square dipyramid, pentagonal orthocupolarontunda, gyrobifastigium, snub disphenoid, and hebesphenomegacorona. (A fun word game: try to use one of these names in everyday conversation.)

What's a hebesphenomegacorona doing onboard the ISS? We're not sure. It was made by Ed Lu or Yuri Malenchenko using paper and tape. One of them fixed it to the top of the Destiny Lab window and took its picture with the cloudy Pacific Ocean in the background.

Were they testing Zalgaller's proof in microgravity? Passing the time on a Saturday morning? Building models of weird solar systems? Maybe they were just playing word games.

Ed: "Yuri, I think I just saw a hebesphenomegacorona in the Destiny Lab."

Yuri: "Are you sure? It looked more like a snub disphenoid to me...."

Today's picture, ISS007-E-05280, was taken on May 15, 2003. Additional images taken by astronauts and cosmonauts may be viewed at the NASA-JSC Gateway to Astronaut Photography of Earth.