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I was sorry to learn Pluto did not qualify as a planet (“New Solar System? Twelve planets and counting,” SN: 8/19/06, p. 115, and this article). Pluto has a diameter comparable with the Earth’s moon. The size of our moon relative to Earth might cause any observer to consider Earth and its moon as double planets. Pluto and Charon could have equal status.

Dennis Rich
Las Vegas, Nev.

Strictly speaking, the original five “wandering stars” (in the Copernican sense) are the only sun-orbiting bodies that can rightly be called planets. In changing the definition of planet , the International Astronomical Union is messing with something much bigger than it is. Think of all the dictionaries, encyclopedias, textbooks, and Web sites that will need revision as a result of IAU’s action.

Virgil H. Soule
Frederick, Md.

The detection of bodies orbiting other stars suggests that the criteria we use to apply the word planet is a matter of broad significance. The criteria accepted by IAU seem to work for our solar system but don’t seem general enough to allow classification of all bodies we may detect.

Charles Stewart
Coral Gables, Fla.

Astronomers have duly decided that Pluto and others should be called “dwarf planets,” but the greater problem is with the term for subordinate satellites. Galileo referred to Jupiter’s subordinates as “moons.” That is really wrong. There is one Moon. We need a term, such as subsat, for subordinate satellites.

Harry Pottol
Sunnyvale, Calif.