"First there were 550, then 110, then 69 and finally seven," he said of being named one of the Mercury Seven finalists in April 1959. He added that it was the happiest day of his life.
He told the students it was "curiosity" that impelled him toward the astronaut program and, yes, he was scared when he went into space.
"But everybody is scared and that makes everybody do better work. We're better drivers on the freeway because we're a little afraid. It's a great motivator," he said.
Carpenter was the first man to have the title of astronaut and aquanaut.
He said he talked with famed French sea explorer and researcher Jacques Cousteau about bringing some of his space experience to the ocean and, on Cousteau's recommendation, he volunteered for the Navy's Sealab experiment and spent 30 days at the bottom of the ocean.
Asked how long he had to train to become an astronaut, he said: "It begins in kindergarten."
The planetarium officially opens this weekend and the astronomers feature, one of three shows to be offered, is $8 for adults and $7 for children. Saturday through Monday, it will be $5 a person.
Saturday is also Kids Day, with a variety of free activities planned to celebrate World Astronomy Day.
JetBlue is a primary sponsor of the planetarium, but spokeswoman Alison Croyle would not say how much money the airline donated. "We never say what we give, but it is to make sure that the children are introduced to engineering."