(Inside Science) -- Every year on the 4th of July, fireworks light up the sky with giant bursts of color and patterns. Today, fireworks are so advanced they turn into shapes like hearts, stars and even smiley faces. But have you ever wondered how they do that?
Fireworks, also known as pyrotechnics in the industry, are older than the American Revolution itself. They have advanced so much, that now we have brighter colors, explosions timed-to-music, and shapes and patterns that wow crowds of all ages.
But those shapes don't make themselves. Here's how it works…
Let’s start with the basic firework. It’s made up of groups of round shells, called stars, and packed with a special mixture of chemicals. The chemicals determine the colors, but the key to achieving a certain explosive shape lies in how the firework's ‘stars’ are aligned inside the shell.
The stars are small plastic pellets that range in size from a pea to a golf ball. When ignited, it’s the ‘stars’ -- or pellets, that create the flashes of color and light.
To make a shape in the sky, firework technicians simply set up the same pattern with the small pellets inside the packaged shell before firing it. Yellow pellets are packed in the shape of smiley faces; red pellets are arranged in the form of hearts. Blue pellets are organized into the form of a star. Any shape you pack inside the firework’s shell will ignite that same shape across the sky.
But certain shapes are tricky. Creating perfect alphabet letters in the sky is still a challenge for the fireworks industry, but they’re working on it -- promising bigger, better explosions that come in all shapes and sizes.
Editor's note: This is a repost of a video that was originally released by Inside Science on June 28, 2016.