Bonfire Night Science: What Makes Fireworks Light Up the Sky?

Exploring the chemistry, physics and fascinating science behind fireworks with practical STEM activities for curious children. Every November, the night sky across the UK fills with colour. Bright green stars scatter overhead. Golden sparks cascade through the darkness. Rockets whistle into the sky before bursting into spectacular patterns, accompanied by bangs, crackles and flashes of light.

For children, fireworks can be fascinating. But behind every colourful explosion is an extraordinary combination of chemistry, physics and engineering.

Why are some fireworks red while others are green? What makes them produce different sounds? Why do we see a flash before hearing the bang? And how do fireworks create those beautiful shapes in the sky?

Bonfire Night provides an opportunity to explore these questions and introduce children to scientific concepts through something they may already be curious about. You don't need to recreate fireworks at home to investigate the science behind them. In fact, some of the most interesting ideas can be explored using simple, safe experiments with light, sound, colour and movement.

Let's discover what makes fireworks work.

What actually happens when a firework explodes?

Fireworks are carefully engineered devices that use chemical reactions to produce light, sound, heat and movement. Although fireworks come in many different designs, aerial display fireworks generally involve several important components.

A lifting charge launches the firework into the air. Inside the firework are small pellets of chemical compositions, often called stars, which produce the coloured light we see.

A timed fuse and bursting charge help determine when the firework opens and how the stars spread across the sky.

When the stars burn, they produce the bright colours and patterns associated with fireworks.

There are several different scientific processes happening almost simultaneously:

• Chemistry: Chemical reactions release energy and produce coloured light.

• Physics: Forces launch the firework, while gravity and air resistance affect its movement.

• Sound: Rapidly expanding gases create pressure waves that travel through the air.

• Engineering: The design and arrangement of components influence the timing, shape and visual effect.

A firework display is therefore much more than a collection of colourful explosions. It is an example of several scientific disciplines working together.

1. Why do fireworks have different colours?

One of the most interesting questions children ask about fireworks is why they produce so many different colours. The answer lies largely in chemistry.

Firework manufacturers use particular chemical compounds, including metal salts, to produce characteristic colours. When these substances are heated, energy can excite electrons in atoms or ions. As electrons move between allowed energy states, light of particular wavelengths may be emitted. Different elements and compounds can produce different emission patterns, which contribute to the colours we see.

Which chemicals produce which colours?

The final colour depends on the chemical formulation and the conditions under which it burns. Some effects also involve incandescent particles emitting light because they are extremely hot. This means that firework colours are not simply created by adding coloured dyes. They arise from the way particular materials behave when energy is released.

Why is blue especially difficult to produce?

Blue is one of the more challenging firework colours to create reliably. Blue-producing compositions commonly rely on light emitted by copper-containing species. The chemical conditions must be carefully controlled because excessive temperatures can interfere with the formation or stability of the species responsible for the desired blue emission. This makes blue fireworks an interesting example of how chemistry and engineering must work together. A substance might be capable of producing a particular colour, but achieving that colour consistently in a real firework requires careful design.

STEM activity: Explore colour using light

You will need: A torch, transparent coloured cellophane or light-filter sheets, and a white wall. Shine the torch through different coloured filters. Observe how the light changes, then try combining filters.

Ask your child:

• What happens when you change the colour of the filter?

• Does the light become brighter or dimmer?

• What happens when you overlap two filters?

• Why might some colours be harder to see?

What children learn: Light, colour, observation and how materials affect transmitted light.

Scientific distinction: Coloured filters selectively transmit and absorb light. This is different from the light-emitting chemical reactions that produce firework colours, but it provides an accessible introduction to investigating colour.

2. Why do fireworks make loud bangs?

Fireworks don't just produce light. They also create a variety of sounds. Some whistle as they travel upwards. Others crackle, pop or explode with a deep boom. To understand why, we need to explore how sound travels. Sound is produced by vibrations that create pressure waves in a medium such as air. When a firework's bursting charge reacts rapidly, it produces hot gases and a sudden increase in pressure. This creates a pressure wave that travels outwards through the surrounding air. When the wave reaches our ears, we hear the bang. The characteristics of the sound depend on the design of the firework and the speed and nature of the pressure changes.

Why do some fireworks whistle?

Whistling fireworks use specially engineered compositions and structures that can generate rapid pressure oscillations as gases escape. These oscillations produce sound at particular frequencies. The result is a high-pitched whistle rather than a single bang. This introduces an important scientific idea: Different sounds are associated with different patterns of vibration.

STEM activity: Investigate sound vibrations

You will need: An empty tissue box and rubber bands of different thicknesses. Stretch rubber bands around the box and gently pluck them one at a time. Younger children should be supervised with rubber bands. Listen carefully to the different sounds.

Ask:

• Which rubber band produces the highest-pitched sound?

• What happens when the band vibrates?

• Does changing the tension affect the pitch?

• Can you see the rubber band moving?

What children learn: Vibration, pitch, sound production and how physical changes affect sound.

For older learners, introduce the concept of frequency: the number of vibrations or cycles occurring each second. Higher-frequency vibrations generally produce higher-pitched sounds.

3. Why do we see fireworks before we hear them?

Have you ever noticed that a firework lights up the sky and then, a moment later, you hear the bang?

This happens because light travels much faster than sound. Light travels through a vacuum at approximately 300,000 kilometres per second. Sound travels through air at roughly 343 metres per second at 20°C, although its speed changes with temperature and other conditions. Over the distances involved in a typical firework display, the light reaches our eyes almost instantly. The sound takes longer to travel through the air. This creates the delay between seeing the explosion and hearing it.

Can we estimate how far away a firework is?

Yes, approximately. If you count the seconds between seeing the flash and hearing the bang, you can estimate the distance. For example, if the delay is three seconds: \[ 343 \times 3 = 1,029\text{ metres} \] That means the firework was approximately one kilometre away. This is only an estimate, because sound speed varies and the timing of different visual and sound effects may not match perfectly.

STEM activity: Firework distance investigation

If your family watches an organised fireworks display from a suitable viewing location, try this observation activity.

1. Watch for a bright aerial burst.

2. Start counting when you see the flash.

3. Stop when you hear its corresponding bang.

4. Record the time.

5. Repeat with several fireworks.

Older children can multiply the number of seconds by approximately 343 to estimate the distance in metres.

What children learn: Speed, distance, measurement, estimation and how scientists use observations to make calculations. This also provides a natural connection to thunderstorms, where we see lightning before hearing thunder.

4. How do fireworks create different shapes?

Fireworks can produce circles, rings, hearts, stars and other elaborate patterns. How is that possible?

The answer involves engineering and the arrangement of the stars inside the firework. In many aerial fireworks, the stars are positioned within a shell so that when the bursting charge disperses them, they create a particular visual pattern. The arrangement of the stars, the direction and strength of the burst, and the way the firework is oriented all influence the final effect. For example, a ring-shaped arrangement of stars can produce a ring of light. However, the pattern may look different depending on the angle from which the audience views it. A circular pattern seen from the side may appear compressed or distorted. This introduces several important mathematical and scientific concepts:

• Two-dimensional and three-dimensional shapes.

• Symmetry and patterns.

• Forces and movement.

• Direction and orientation.

• Perspective and observation.

STEM activity: Design a firework pattern

You will need: Black paper, coloured paper circles or stickers, a pencil and a ruler. Ask your child to design a firework burst using coloured dots to represent stars. Challenge them to create:

• A symmetrical circular pattern.

• A ring of stars.

• A five-pointed star.

• Two overlapping patterns.

• Their own original design.

For older children, ask how the pattern might appear if viewed from a different angle. What children learn: Symmetry, geometry, spatial reasoning, patterns and engineering design.

5. What makes fireworks travel upwards?

Before a firework produces its colourful display, it often needs to travel high into the sky. This involves forces and motion. Aerial fireworks are launched using expanding gases produced by a chemical reaction. These gases exert forces that accelerate the firework upwards. Once the firework has been launched, gravity acts on it throughout its flight, slowing its upward movement and eventually causing it to fall unless other forces intervene. Air resistance also affects its motion. This gives us an opportunity to introduce some of the ideas associated with Isaac Newton's laws of motion.

What forces are involved?

Gravity: Pulls objects towards Earth.

Thrust or launch force: Provides the force that accelerates a firework upwards.

Air resistance: Opposes motion through the air.

Children don't need to understand complex equations to begin investigating these concepts. They can explore what happens when objects are pushed, released, thrown or allowed to fall.

STEM activity: Balloon rocket investigation

You will need: A balloon, string, a drinking straw and tape.

Thread the string through the straw and secure it between two points. Attach an inflated balloon to the straw, then release the balloon without tying it. As air escapes backwards, the balloon moves forwards along the string.

Ask your child:

• What makes the balloon move?

• What happens if the balloon contains more air?

• Does the angle of the string affect the movement?

• How could we measure the distance travelled?

What children learn: Forces, movement, action and reaction, measurement and fair testing.

The balloon rocket and an aerial firework are not identical systems, but both offer opportunities to investigate motion caused by gases moving in a particular direction.

6. Why do fireworks sparkle and crackle?

Not all fireworks produce large colourful bursts. Some create glittering trails, sparkling fountains or rapid crackling sounds. These effects depend on the materials used and the way they react. Bright sparks are often produced by small particles of hot material emitting light as they burn or cool. Some compositions produce repeated small bursts, creating a crackling effect. Different materials and particle sizes can influence the appearance and duration of the sparks.

This is an excellent opportunity to discuss the difference between light produced by hot materials and light emitted through particular atomic or molecular processes. Both contribute to the visual effects of fireworks, but they are not exactly the same.

STEM activity: Investigate reflective materials

Collect safe everyday materials such as aluminium foil, white paper, dark paper and a mirror. Shine a torch towards each material and observe how it reflects light.

Ask:

• Which materials appear brightest?

• Which reflect light in a particular direction?

• What happens when you crumple the foil?

• Does the angle of the torch change what you see?

This experiment investigates reflection rather than the light-producing chemistry of fireworks. It helps children distinguish between objects that produce light and objects that reflect light.

7. What happens to fireworks after the display?

Fireworks provide a fascinating scientific spectacle, but they also raise important environmental questions. Firework displays can release gases and fine particles into the air. Depending on the compositions used, some emissions may contain metals and other substances. Fireworks can also produce litter and noise that affects people, pets and wildlife. This creates opportunities for older children to investigate the relationship between scientific innovation, celebration and environmental responsibility.

For example, you might explore:

• How does air quality change around large firework displays?

• Why might loud noises affect animals differently?

• What alternatives exist to traditional fireworks?

• How could engineers design displays that produce less pollution or noise?

• What are the advantages and limitations of drone light shows?

These questions encourage children to recognise that scientific and engineering decisions often involve balancing competing priorities. A technology can be impressive and enjoyable while still having environmental or social consequences worth investigating.

STEM challenge: Design a celebration of the future

Ask your child to imagine they have been commissioned to design a public celebration. Their challenge is to create something that is:

• Visually exciting.

• Suitable for a wide audience.

• Mindful of noise.

• Considerate of wildlife.

• Designed to minimise waste.

They could choose projection mapping, coordinated lights, drones, illuminated installations or an entirely original idea.

Older learners can research costs, energy use, engineering constraints and potential environmental impacts.

The aim isn't to assume one technology is automatically better in every respect. It is to encourage children to evaluate evidence and explain their decisions.

8. Exploring Bonfire Night through history

Bonfire Night is also an opportunity to connect science with history.

In the UK, 5 November commemorations are associated with the Gunpowder Plot of 1605, when a group of conspirators planned to destroy Parliament. Guy Fawkes was discovered guarding explosives beneath the House of Lords. The failed plot subsequently became associated with annual commemorations, bonfires and, eventually, fireworks. The history is more complicated than the familiar story of Guy Fawkes alone.

It involves religious conflict, political power, persecution, loyalty and the relationship between the monarchy and Parliament.

For younger children, the focus might simply be on understanding that Bonfire Night is a historical tradition.

Older children can investigate:

• What happened in 1605?

• Who was involved in the Gunpowder Plot?

• Why were religious tensions so significant?

• How do historical events become annual traditions?

• How have Bonfire Night celebrations changed over time?

This is also a useful opportunity to discuss the difference between historical facts, interpretations and traditions that develop long after an event.

History becomes more meaningful when children understand not only what happened, but why people remember it.

9. Adapting Bonfire Night learning for different ages

Not every child needs to investigate the same scientific ideas in the same depth. A four-year-old exploring colour and sound is engaging with important scientific concepts, just as an older learner investigating emission spectra or calculating sound speed is.

The key is to build on what children already understand.

These are broad age guides rather than fixed limits. Adapt activities to your child's prior knowledge, interests and support needs.

10. Five questions to ask your child during a fireworks display

One of the simplest ways to encourage scientific thinking is to ask thoughtful questions. You don't need to know every answer immediately.

Try asking:

1. Why do you think that firework was green instead of red?

2. Why did we see the light before we heard the sound?

3. What forces helped the firework travel upwards?

4. How do you think the firework made that circular pattern?

5. What would you change if you were designing a quieter display?

Allow your child time to think. Encourage them to explain their reasoning, make predictions and ask further questions. If neither of you knows the answer, investigate it together afterwards. That is an important part of scientific learning too.

A note on firework safety

Fireworks contain energetic chemical compositions and can cause serious injury if handled incorrectly.

Children should never attempt to make, dismantle, modify or ignite fireworks as a science experiment. All the activities suggested in this article are intended as safe alternatives for exploring the underlying scientific concepts, with appropriate adult supervision.

For actual fireworks, follow current UK safety guidance, attend professionally organised displays where possible and keep children at a safe distance.

You can find further advice through the Royal Society for the Prevention of Accidents (RoSPA) and GOV.UK fireworks guidance.