CHAPTER 1 PLUTO In 1929 a young man began working for an observatory His name was Clyde Tombaugh His job was to find a new planet He studied pictures of the night sky for a year Then in 1930 he made a big discovery He found a tiny speck that moved through the sky like a planet He discovered what came to be called Pluto
The Three Rules for Planets RULE ONE It must orbit a star RULE TWO It must be mostly round RULE THREE Its path must be clear of smaller objects
Defining Planets For 76 years people called Pluto a planet Then in 2006 that changed Scientists had found other bodies in space similar to Pluto Some of them were even larger than Pluto Scientists didn't feel they should all be planets So they made three rules for planets Objects that only follow the first two rules such as Pluto would be dwarf planets
