Guy Fawkes Night: The chemistry behind fireworks

With bonfire night on the horizon, scientists reveal just why fireworks are differently coloured and what this can teach us about stars in space.

Elements commonly found in salts are used to make the colours in fireworks. The colours are caused when the elements are heated, causing them to release light in different colours, from bright blues to deep reds.

Scientists, according to a statement from Warwick University, use these chemistry phenomena when making multi-coloured fireworks and harness them to investigate stars in the night sky, according to a statement issued by the University of Warwick.

Alex Baker, Assistant Professor, Department of Chemistry, University of Warwick, said: “Fireworks are made of different chemical elements – including potassium and sodium. The atoms of these elements house even smaller, negatively charged electrons.

“When these elements are heated, such as by someone lighting a firework with a flame, the electrons become ‘excited’. This means they have increased energy resulting in them jumping from their original location (known as a ‘ground state’), to another ‘excited state’ location within the atom.

“As electrons drop back down from their excited state, they release the energy they initially absorbed – in the form of heat and light. What is particularly interesting is each electron drop, and the release of light, is unique to each element.

“Atomically, bright blue and violet lights are highly energetic, the electrons have ‘dropped’ a relatively long distance (albeit in tiny subatomic scales). Red light is less energetic, dropping shorter distances.

“We call this range of colours a spectrum – and we see spectrums all the time in everyday life. Rainbows are the most common examples of spectrums; so is a prism, which splits light into its individual components (the colours of the rainbow).

“If fireworks are made of potassium elements, they burn with blue and violet light; sodium as red. Boric acid, barium or copper salts produce green colours. Magnesium produces white.”

What can fireworks tell us about the stars?

Astrophysicists can apply the science of firework colours to observing stars in the night sky.

Teams of researchers including those at The University of Warwick plot graphs and charts which show the intensity of light emitted by stars over energy wavelengths. Like fireworks, each element present in stars correlates with colours on the rainbow spectrum. This technique, known as spectroscopy, tells us what elements stars are made of.

Professor Pier-Emmanuel Tremblay of the Department of Physics at the University of Warwick said: “Spectroscopy offers us a fantastic tool to learn more about the Universe. Each chemical element or molecule provides a unique type of code on the spectrum, a bit like a barcode when shopping.

“This means we can identify elements in the atmospheres of stars, working out exactly what gases are present. Our own Sun, for example, is rich in Hydrogen and Helium, with traces of many heavier elements. We can even work out the temperature, density and magnetic fields based on the principles of spectroscopy.

“If there is life out there, spectroscopy is one of the key tools we could use to find it.”

So when you see a fireworks this bonfire night – be sure to impress your friends with the atomic reasons for their bright colours. And know that the same science is being applied to understand more about our universe.