Every year on the Fourth of July, one of the most breathtaking fireworks shows lights up the skies over the Statue of Liberty and the New York City skyline. While many marvel at the spectacle, the underlying science, particularly quantum physics, often goes unnoticed.

This year, July 4, 2019, is significant for multiple reasons: it marks aphelion, the point in the Earth's orbit where it is farthest from the Sun; it commemorates the 243rd anniversary of America's independence; and it represents a day when the United States sets off more fireworks than any other nation.

Whether you are a fireworks enthusiast, a professional pyrotechnician, or simply an observer, the principles of physics that govern these displays are universal. Each firework comprises four essential stages: launch, fuse, burst charge, and stars. Quantum physics is crucial to the functioning of each stage.

The launch stage initiates the firework's journey with an explosion that provides the lift. For over a thousand years, the fundamental ingredients of fireworks have remained consistent: sulfur, charcoal, and potassium nitrate. Sulfur naturally occurs in volcanic areas, while potassium nitrate can be found in substances like bird droppings.

Charcoal, unlike the briquettes used for grilling, is the carbon residue from pyrolyzing organic materials such as wood. When the moisture is removed from the charcoal, these ingredients can be ground together to create gunpowder, which is rich in oxygen due to the presence of potassium nitrate.

Mixing these components generates significant energy stored within molecular bonds. However, a more stable arrangement can be formed. When ignited, the raw materials combust at high temperatures to produce solids like potassium carbonate and gases including carbon dioxide and nitrogen.

The ignition of these materials requires only a small heat source, such as a match. The resulting reaction is a rapid deflagration, advantageous for propulsion. The rearrangement of atoms allows energy to be released, perpetuating the reaction. Quantum physics is essential for harnessing this stored energy.

Upon the initial energy release, known as the lift charge, two primary effects occur:

1. The lift charge provides an impulse that accelerates the firework upwards within its launch tube.
2. During combustion, the lift charge ignites the main fuse, which will detonate the firework when it reaches the gunpowder.

The upward acceleration must ensure the firework reaches a safe height for detonation, while the timing of the fuse is critical for an explosion at the peak of its ascent. Smaller fireworks may require heights of 200 feet (60 m), while larger displays, such as those seen in New York, can demand altitudes exceeding 1000 feet (300 m).

The fuse, which is ignited by the lift charge, serves as the second stage. Most fuses utilize a similar black powder reaction to the lift charge, but are designed to delay ignition, often wrapped in a textile coated with wax or lacquer. This ensures they function under various weather conditions.

The textile is crafted from woven strings, controlling the burn rate based on material properties and design. Fuses may take 30 seconds to burn a foot or can burn rapidly at much greater speeds.

The third stage, the burst charge, determines the distribution of stars within the firework. Generally, higher launches and larger shells necessitate more substantial burst charges to disperse the interior contents effectively. The burst charge might consist of simple black powder or more complex mixtures that control the explosion's intensity and spread.

The most captivating stage occurs when the stars ignite. The burst elevates the internal temperature, creating the light and colors of the display. Various chemical compounds can be used in the stars, and when heated, they emit light at different wavelengths, producing the vibrant colors we see.

The mechanism behind these colors involves exciting electrons within atoms or molecules. When these electrons transition to lower energy levels, they emit photons, resulting in the visible spectrum. Elements like sodium, for instance, emit a distinct yellow glow due to their specific emission lines.

The variety of colors in fireworks comes from different elements and compounds, including barium, copper, and strontium, each producing unique hues. The interplay of these materials creates a full spectrum of color with only a handful of compounds.

It's fascinating to note that the color perceived by the human eye may differ from the actual light emitted. For instance, a violet laser emits photons at a specific wavelength that directly corresponds to the violet spectrum. However, on a computer screen, that color can be represented without emitting violet photons.

The human perception of color is constructed from the combined responses of three types of retinal cells sensitive to different light wavelengths. Thus, creating a fireworks display isn't merely about generating specific wavelengths, but rather about evoking the right sensory responses in our eyes and brain.

Fireworks may seem like straightforward explosive devices, but a closer look reveals the intricate quantum physics that underpins each reaction. By adding elements such as propulsion, one can create dazzling effects. Enjoy your Fourth of July celebrations, fully aware of the science that makes these magnificent displays possible!

Starts With A Bang is now featured on Forbes and republished on Medium, thanks to our Patreon supporters. Ethan is the author of two books, "Beyond The Galaxy" and "Treknology: The Science of Star Trek from Tricorders to Warp Drive."