How did the expression begin? No one seems to know for sure.
But an official of the American space agency--NASA says the expression just grew.
"It grew," he says, " because rocket scientists probably are the most intelligent people around."
Not everyone would agree. Some people might be considered more intelligent than rocket scientists.
For example, a person who speaks and reads 15 languages or a medical doctor who operates on the brain.
Still many people would agree that there is something special about scientists who build rockets.
Maybe it has to do with the mystery of space travel.
Moving pictures from before World War Two showed a man named Buckrajors landing on the planet Mars.
He was a hero who could defeat any enemy from outer space.
