An image from NASA's Hubble telescope looks down a long corridor of galaxies -- and billions of years back in time.

NASA via AP

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Star Power

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When he stands before this sixth-grade class, the geek in Tyson comes out, but so does the showman. His brain seems overstuffed not just with facts -- temperatures, elements, astronomical history, particulars about galaxies, trivia about time -- but strategies to explain those facts.

"I brought a piece of the universe with me," he says at the outset.

Ooohs all around.

The piece, it turns out, is a dark, jagged chunk of an asteroid. It is 5 billion years old and weighs 12 pounds, but because it's so small and dense it seems heavier.

"Who here is strong?" Tyson asks.

One by one, kids take turns standing in front of the class and trying to hold the chunk in one outstretched hand without the arm dipping, which proves comically difficult to do. There's talk of boiling points, freezing points and the surface of Mars -- where water boils and freezes at the same temperature, which Tyson describes as "pretty freaky."

The kids have questions.

"What would happen if you touched your hair with dry ice?" asks a girl.

"It would get brittle and you could snap it off," Tyson says. "If your ears get frozen, you could snap them off like potato chips."

Ewwww! shouts the class.

"That is so cool," counters one undaunted youngster. "Would you bleed very badly?"

Tyson never gets to answer this one, because he's interrupted.