Multicolored explosions of glittering stars delight and thrill people across America every Fourth of July. While dazzled by the display, some may be wondering “what are fireworks?” as the smoke clears from the sky.

The science of fireworks can be traced back 1,000 years — from earlier primitive methods to modern technology transforming the explosions into more complex patterns using different types of metals, fuses and chemical reactions.

What Are Fireworks?

If you guessed that fireworks work in a process similar to a bullet being fired, you’re mostly correct. That’s how Chinese alchemists created the first fireworks when they put bamboo stalks filled with gunpowder into a fire pit. Often, the fireworks were used to ward off evil spirits at celebrations, according to Time.

Fireworks took on a different meaning when they were introduced to Europe in the 13th century, quickly becoming a staple for major celebrations, Time explained. Pyrotechnicians, looking to wow the crowds, discovered ways to add colors, and soon large fireworks displays were used to mark major events or military victories.

Today, instead of bamboo stalks, we use explosive aerial shells combined with special oxidizing chemicals that help propel the shell into the sky. Fireworks are sent airborne through packaging and chain reactions. A mortar houses the firework, and a separate lifting charge sends the firework skyward. Inside the mortar is a shell containing “stars” — which produce the colors and points of light — as well as gunpowder and timed charges to create patterns. A firework with a smiley face pattern is created by stars carefully placed within a shell to create that recognizable expression in the sky, according to Popular Science.

Where Do the Bright Colors Come From?

The bright colors you see flash across the night sky are produced through different metal salt combinations.

Strontium salts produce red fireworks, calcium salts create orange fireworks, sodium salts produce yellow fireworks and copper chloride yields blue fireworks. Different compounds create different shades of color to add variety, and metal salt combinations produce different colors, similar to how mixing primary colors (say, red and yellow) produces a secondary color (orange). Purple fireworks, for example, are created through a mixture of copper and strontium. To add some flair to the spectacle, aluminum powder creates the bright white flashes seen in sparkler-type fireworks, as noted by Popular Science.

Who knew the science of fireworks was so complicated?

In the Air … and in Space?

Considering the dazzling display, surely fireworks could be seen in space? After all, man-made objects like the Great Pyramids of Giza, dams and bridges can be seen by astronauts aboard the International Space Station.

As it turns out, fireworks can be seen from space, although they only appear as tiny specks of light. National Geographic reported that NASA astronaut Scott Kelly said that he in fact saw fireworks during his time in space. However, if astronauts wanted to have their own fireworks display, it would be feasible, although there would be no thunderous boom associated with the explosion in the vacuum of space.