Astronomers from all over the world, meeting in Prague in August 2006, have voted to no longer call Pluto a planet.

The scientists agreed that for a celestial body to qualify as a planet:

• it must be in orbit around the Sun

• it must be large enough that it takes on a nearly round shape

• it has cleared its orbit of other objects

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Pluto was disqualified because its highly elliptical orbit overlaps with that of Neptune. It will now join a new category of dwarf planets.

About 2,500 scientists meeting in Prague have adopted these new guidelines, and now we will have to talk about a solar system with only eight planets.