Kaitlyn was practicing her pitching at the baseball field.
She reached into her bucket for another ball.
Suddenly—beep, beep, beep!
A big truck backed slowly onto the field.
"Hey!" Kaitlyn thought. "What's that doing here?"
A man got out of the truck. "Sorry," he said.
"We need to set up here for tonight's fireworks display.
You'll have to move somewhere else."
"The Fourth of July show is still hours away," Kaitlyn said.
"Can't I practice my pitching some more?"
"I'm afraid not," the man said.
"It takes several hours to set up a fireworks display."
By now more men had arrived.
They were moving wooden racks and boxes onto the field.
Kaitlyn sighed. She looked closely at a rack.
It held short plastic pipes. "Those are fireworks?"
"Nope," the man said.
"Those are cannons that shoot the fireworks into the sky."
He opened a box and took out a brown object wrapped in plastic.
It was about the size of a baseball and looked like a little bomb.
"This is a firework shell."
"What's inside of it?" Kaitlyn asked.
"I'll explain," said the man.
He set the shell gently back into the box.
Then he bent down and drew a big circle in the dirt.
"A shell is filled with little balls of gunpowder.
Pyrotechnicians, like me, call these balls 'stars.'"
He picked up some baseballs and formed a pattern inside the circle with them.
"The pattern of the stars gives a firework its shape."
"What gives a firework its color?" Kaitlyn asked.
"Magic!" The man laughed.
Kaitlyn didn't. She really wanted to know the answer!
"Well, the magic of science," the man added quickly.
"Pyrotechnicians add chemicals to the gunpowder stars.
When these chemicals burn, they make different colors.
Like chemicals containing copper, for example—can you guess what color they make when they burn?"
Kaitlyn pulled a penny from her pocket and glanced at it. "Orangish brown?"
"Nope!" the man said.
"Chemicals with copper make blue.
Chemicals with calcium make orange."
Next the man drew a square attached to the circle.
"There's even more gunpowder here at the bottom of the shell."
He drew a long line from the center of the circle.
"This is the fuse. It's a string that lights the shell.
When the shell is in the cannon, the fuse lights the gunpowder at the bottom of the shell.
That explosion pushes the shell out of the cannon and into the air."
"The shell doesn't burst inside the cannon?"
"Nope. The fuse continues to burn in the air.
Finally it explodes the shell and lights the stars.
That's when you see the firework in the sky."
"Awesome," Kaitlyn said.
"Hmm. I guess you do have a lot to do before tonight."
"Right. It's a big show with many fireworks!
And we have to work carefully and safely.
Working with fireworks is very dangerous."
The man helped Kaitlyn gather her baseballs.
"Are you going to watch the display tonight?" he asked, dropping the last baseball into her bucket.
Kaitlyn smiled. "I can't wait!"