Monday, August 21, 2006

By any other name

What a stir! The proposal by the International Astronomical Union to redefine what constitutes a "planet" made front page news in the major dailies. The story is all the buzz. Nine planets become twelve! Our familiar solar system turned upside down!

Hey, we take our planets seriously, and we have a lot of affection for little Pluto. Ceres? UB313? Who are these upstarts anyway?

What's really going on is a straightening out of nomenclature: making language conform to our evolving understanding of what the solar system is and where it came from. Pluto is half the size of Mercury. Ceres -- between Mars and Jupiter -- is half the size of Pluto. Why call Pluto a planet and not Ceres? The choice is arbitrary. And what about new objects beyond Pluto that have been and will be discovered.

Where do we draw a line that is not arbitrary? A planet -- according to the new definition -- is a non-stellar object that orbits a star and is large enough for gravity to give it a spherical shape. Potato-shaped, not a planet. Spherical, it makes the list.

The great 18th-century botanist Karl von Linne, better known by his Latinized name, Linneaus, taught us that nothing is well described unless well named, and that nothing is well named until well described. Naming and exact description go hand and hand, and, if carefully done, reveal the patterns implicit in nature itself.

Not long after Linneaus proposed his new nomenclature for biology, the Frenchman Antoine Lavoisier set out to do much the same thing for chemistry. In the preface to his great work, Elements of Chemistry, Lavoisier quotes the philosopher Condillac: "We think only through the medium of words...The art of reasoning is nothing more than a language well arranged."

Lavoisier then goes on to tell us: "Thus, while I thought myself employed only in forming a nomenclature, and while I proposed to myself nothing more than to improve the chemical language, my work transformed itself by degrees, without my being able to prevent it, into a treatise upon the Elements of Chemistry. "

That's what's going on with the International Astronomical Union: Reorganizing nomenclature to conform with our developing understanding of planetary systems -- to consolidate present knowledge and to facilitate future research. The rest of us will just have to adjust.