How science helps light up the sky on the Fourth of July
From dazzling reds and fiery oranges to vibrant greens, deep blues, and rich purples, fireworks light up the sky every Fourth of July, drawing crowds from all over.
Life-threatening July 4 heat wave intensifies over 260M across Eastern US
The dangerous heat is intensifying Friday as millions are expected to attend outdoor events marking America's 250th birthday, with feels-like temperatures forecast to reach between 100 and 115 degrees along the Northeast and Mid-Atlantic coasts.
As America’s 250th birthday approaches, communities across the country are preparing for one of the holiday's most beloved traditions: fireworks.
From dazzling reds and fiery oranges to vibrant greens, deep blues, and rich purples, fireworks light up the sky every Fourth of July, drawing crowds from all over.
But those colors aren't created by chance, they're the result of science.
Fireworks lit up the sky behind the Statue of Liberty during the Fourth of July. (Photo by Lokman Vural Elibol/Anadolu via Getty Images / Getty Images)
Every firework is created from metal salts. The colors come from a different compound that contains metal and non-metal atoms packed inside the firework shell.
Chemicals like potassium nitrate, sulfur and charcoal are used to help the fireworks burn.
Nitrates, chlorates and perchlorates provide oxygen for the combustion, while dextrin is utilized as a starch that holds it all together.
Fireworks light up the sky over the East River and Brooklyn during the Macy's Fourth of July fireworks show on July 4, 2025, in New York City. ((Photo by Gary Hershorn/Getty Images) / Getty Images)
When the firework is launched and ignited, the intense heat causes the atoms in those compounds to produce colors.
As the atoms return to their normal energy state, they release light at specific wavelengths, producing the colorful displays seen overhead.
For example, strontium compounds create bright red fireworks, while calcium produces orange-colored fireworks. Sodium is responsible for yellow bursts, barium creates green, copper generates blue, and a combination of strontium and copper can produce a purple effect.
Fireworks during the annual Freedom Over Texas festival on the Fourth of July, Thursday, July 4, 2024, in Houston. (Ishika Samant/Houston Chronicle via Getty Images / Getty Images)
Firework designers carefully mix these compounds together to create both the desired colors and dazzling visual patterns.
So, whether you're watching a neighborhood display or a large-scale celebration, you’ll know that every colorful explosion is a combination of science.